Mark Romero 2

S5 for me and it keeps everything even more incestuous other than the batteries.

I own a G6, G80 (a Euro spec G85) and G9. Never used a G7 or GH5.
Re. the G85 - it's a very good hybrid camera, but compared to the GH5 (and the G9) it uses the older 16MP sensor, has cropped 4k and noticeably inferior 1080p. It's a smaller, lighter and cheaper camera though, and I think it might make an excellent 'serious' but maybe less intimidating camera for your son.
Also Panasonic have changed their colour science - for the better - over time, so it's probably going to be harder to match something older like a G7 to the S1.
If you can live with the 30 minute (10 mins for 4k 60p) record limit, a G9 is cheaper than a GH5 and has better IBIS and autofocus, plus 10-bit video capability. The V-log L update can also be added to it.

Mountain biking at night without lights is an interesting way of defining how good your own personal "night vision" is!
Don't think I'd ever do that myself. But I'd happily run at night, even off road with no LED lights. (heh, back in my heyday of running, LED lights barely existed! At least not for this poor impoverished boy, thus I'd often be running off road at night for long training sessions)

Yep. Or at least how I saw it and was considering.
But then I looked at the price of an S1 now vs an S5 and weighed up what the S1 would bring me that I needed over an S5 and the answer was unlimited recording.
And that was not a sufficient enough answer when I factored in all the other 'stuff' I was getting with an S5, mainly in the size & weight department.
I am not exactly uber-obsessive about every last nanogram etc, but it all counts and adds up.
Ultimately it's what works for our own individual situations and these things can depend on what kit you already have, but if starting from scratch... Well that offers up more choice.

Having said that, I am not ruling out going with 3x S5's and 1x S1 come next Spring instead of 4x S5's, purely to have that S1 in the dedicated static no record limits, video role...

Best option I think. I still think with the firmware update due in 2021 for the S1 that it will outperform a bit the S5, but considering your requirements (size mainly) it should be a good option to have the S5. I personnally enjoy shooting with the S5 as it's so lightweight. But then when I grab my S1H again I'm feeling at home, I like the grip, the good size with the big lenses, etc. Each body has its purpose; and that's great to have this flexibility.
 

Seriously I think the S5 would be the best option. Same mount, same sensor, same everything except for the batteries and the HDMI!
I have the S1H and I chose to buy the S5 for my B-cam/gimbal cam. It's way better to have same bodies, same menu systems, same sensor size, same (kind of) low light performance, same dual ISO, etc.  Of course that's my opinion.

But why wouldn't you just use your S1 for stills?

Remember it is no big deal to shoot rec709 on for the boring long interviews / ceremonies / speeches / talking heads that you're shooting. 
As you're got the time and set up to nail your exposure and white balance. And you're not going to be going crazy "arty" looking with these shots in the edit anyway. 

Leave shooting in log / raw / whatever for the B Roll / flashy stuff when you're just shooting the single A Cam by itself.
You do get a better sensor in the G85, but the G7 has no recording limit as well (with the setting tweak), and IBIS doesn't even matter when it is only ever going to be used on a tripod!!

In the end, it comes down to how much you want to save every last penny that you can or not. Otherwise you'd just go get a Panasonic S1H as your C Cam 😉
 

Sure thing, tons of examples on my vimeo, https://vimeo.com/user16941419/videos 

Pretty much anything two-camera is S1 A-cam and wide, GH5 b-cam, close-up angles. 


But here are a couple random ones if you don't feel like digging. I'm not a pro colorist by any means, most of my projects have very fast turn around so I get them "good enough" and don't always go for a 100% perfect match between cameras, but I don't they look glaringly different or anything, even in higher DR-situations. 
 
 

I have been using an S1/GH5 combo for probably close to two years now, it's a very winning combo, primarily for your same use case, mostly talking head/interviews and corporate work. No need to over think it, I shoot both in V-Log pretty much all the time and they are quite easy to match, typically I use the GHAlex LUT and it looks awesome. 

If shooting in Vlog on the S1, the colors on the G85 aren't really going to be doing you any favor in terms of matching. Of course you could shoot both in CineD. Fast lenses are a good option to workout low light limits on M43 but good fast glass is expensive. Cheaper lenses that are super fast are generally not the most usable wide open. But I guess again the question is do you actually need low light performance for interviews? 
 

Swapping AF and low light for unlimited recording and colour matching seems like a good trade-off if you're doing interviews and weddings, especially for a B-camera.
Also WRT low light, the MFT cameras can get very passable low-light performance if paired with a fast lens.  I have above average night vision (I can easily go off-road mountain bike riding with no lights if there's a full moon) but the GH5 and f0.95 lens combo can see in the dark better than I can.
The other low-light advantage of MFT is that on an f0.95 lens it gets the exposure value of T0.95 but a DoF equivalent to a FF at F1.9, so better exposure without the razor-thin DoF.
I'd suggest having a think about the various interview configurations that you might use and then working out what the minimum requirements would be for those setups, in order to avoid buying gear you don't end up using.

In terms of 8-bit, concentrate on getting it as right in-camera as you can.  All the 10-bit vs 8-bit tests that identified differences (many didn't) only had issues when the image was pushed by a decent amount, so the better you get it in-camera the less you have to push it around and the better the image will be.
Matching colour is a matter of:
choosing the same colour profiles on all cameras setting the WB and exposures properly using a colour checker once per setup You can do your homework and record a colour checker on all cameras in controlled conditions, then make an adjustment to match the lesser cameras to the better one, and make it a preset so you can quickly apply it.  Then when you're working on actual projects all you have to do is tweak slightly, if anything at all.
Yes, I realise that this means you will be shooting a rec709 type profile on your best camera, but this is intentional to match colour profiles, and also it will help you get a good quality image in post.  I use the GH5 as my A-cam and shoot the 1080p All-I 10-bit 422 modes, and just recently I swapped from shooting HLG to shooting in Cine-D.  Extrapolating from the principle of "the less you mess with it the further you are away from the image breaking" I no longer take my 10-bit image and radically push/pull the bits around in the HLG->rec709 conversion, so now when I get my 10-bit Cine-D images out of camera the bits are nice and thick and almost exactly where I'll end up putting them in the final grade.
@Ironfilm makes a good point about using the kit lens on a second / third angle, as the kit lenses are nice and sharp when stopped down a bit, and can also be pretty good when at their longest focal length and wide open, especially if it's an angle you're not going to go to for long or many times in the edit.

Again, think carefully about how are you going to be using these B / C Cams on small corporate content shoots?

I've done sound on lots of these types of shoots, and they're almost always single camera shoots. Is it out of lack of confidence you'll not get the coverage from just one camera, or you fear you might miss out on a vital moment in the IV while you're switching up shot sizes on your main cam? Consider how much you might be harming the quality of your work by spreading yourself thin across three cameras vs just having one, and the compromises you're making to ensure the 2nd/3rd angles look good too. 

With a little tweak the G7 can have unlimited recording too, google it. 
As for 8bit, again remember the very specific use case we're discussing here: as B & C Cam for wedding ceremonies / speeches. 
This is low budget sh*t which you're going to be using SOOC or near to it. These cameras are just for bulking out the long form edits to give you coverage. 8bit is fine. 

Especially as @Mark Romero 2 mentioned weddings, I'd strongly consider getting a third camera. (and with @kye's "two is one and one is none" principle, you ought to have four cameras!)

If you know your specific uses cases well, such as: "I'll only use my B Cam (& C Cam) for wiiide / mid wide shots on a tripod for planned out shots in at least moderately well lit conditions" (which is the case for all interviews, they'll be well lit, and I'd even say for weddings too. As no, wedding are not "extreme low light" scenarios. Not by 2020 standards. Sure weddings demanded "good low light cameras" back in the early 2000's when standards of what is "good at low light" was different. But this is 2020! You won't have troubles using MFT whatsoever for your multicamera setups for the ceremony and speeches. Sure, later in the evening when it gets dark and they're partying, good low light capabilities are beneficial. But by this point in time you're no longer rolling multicamera setups for hours at a time, you're getting B Roll with your A Cam instead for the edit)
Thus you could have your Panasonic S1 as your A Cam, and two secondhand Panasonic G7 for dirt cheap, one with the cheap SLR Magic 8mm and the other simply with the kit 14-42mm lens. (perhaps throw in the cheap Panasonic 25mm f1.7 lens, "just in case". Your total lens investment is still very very minimal, thus doesn't so matter much you're spreading yourself thin across two lens mounts of MFT & L Mount)

As much as I am a fan boy of MFT, I'd lean towards spending the extra for a Panasonic S5 (or a second secondhand S1) over a GH5. 

Because it is smart for all your cameras to share the same mount, and of course you'll get an even closer match in colors between your A and B cam. 
(bit different matter if you were asking about a G7 as your B Cam? As the cost savings there are so huuuuuge)

Also, stop buying EF mount glass. 

I second everything that @IronFilm said.
Now is a good time to consolidate to one lens mount as you're selling lenses anyway.  This folds into a lens strategy where you should be able to use the same lenses across both cameras, but without having duplicates, which typically means having the same sensor size.
For example, if you want a variety of shots in your Multicam setup then you want a different FOV from the two cameras.  Typically that would mean having a mid-shot on the A-cam and either a wider shot on B-cam, or a tight shot on the B-cam, and is often done with a 24-70 / 16-35 or 24-70 / 70-200.
If your B-cam was an MFT then you'd either have to have a second 24-70 to get a tighter shot with the crop sensor, or you'd have to use a specialist MFT wide lens like a 7-14mm to get something that was actually wide, but then that's a lens you can't use on your A-camera. 
The other advantage of having cameras of the same sensor size and common lens mount is that everything is a backup for everything else.  If a body dies then you have a second body that can use any of your lenses.  If a lens dies then you have access to every other lens on that camera.
In the spirit of "two is one and one is none" you might consider buying a very cheap third body in case one body dies, which would leave you with a dual-camera setup in that case.  I don't know how you shoot and edit so you could always cut up the interview with B-roll if you only had one camera for the interview, but it's worth considering.  In terms of a third body, something with good 1080p would probably be the way to go, which typically means older and smaller sensor.  In that situation you'd want to get something that required as little extra peripherals as possible, for example, using compatible power solutions, lenses, etc.  That might be where a G7 or something comes into play, where you can use the 70-200 on your main camera and the 24-70 on the backup camera as a mid shot, perhaps positioned further away, or go to 70 and without a speed booster it would be a tight shot.
I'm employing this strategy in my work.  My main setup for travel film-making is a GH5 combined with a Sony X3000 action camera and next trip I will probably buy a GH3 as a second / backup body.  It will take the same lenses, can be used as a second angle if required (either for real-time or time lapses), and if my whole main setup of GH5 goes in the drink (for example) then I can easily replace it with the GH3 and the only overheads of the GH3 will be to carry an extra 3.5mm on-camera mic, USB battery charger and a couple of batteries, and a 14/2.5 lens as replacement to my 17.5/0.95 main lens.  If my X3000 dies then I can use my 7.5/2 lens on the GH5 or on the GH3 to replace the FOV.  I would lose the waterproof abilities of the X3000 but that's the price of a camera dying on a trip.

I may get a maxed out Mac Mini M1 for my company. 
I’m looking at 27-32” monitors and the amount of options is staggering. It’s confusing to say the least. 
It will be used for editing and grading for brand and music video work. 
Budget is up to £1k or maybe a bit more if it’s worth it.
What do you recommend? 

The GH5 is your cheapest and best bet. Of course it can't keep up with the S1 beyond 3200 iso and the dynamic range is more limited. However dynamic range isn't as important for say a close up B cam shot and I am guessing you usually light your interviews. 

The Fuji is a great deal and the image is a step up from the GH5 but the record limits suck for interviews. 

If you can get a used GH5 for under 1k I think its a good option. The 25mm 1.7 might be a good option. The rokinon/samyang 12mm f2 is a good wide angle option if can deal with a manual lens.

The Viltrox is a fine option. Wide open the viltrox is soft that is the one downside. Lens Turbo speedboosters are the best in terms of low budget ones, but they are fully manual. 

Vlog L and Vlog do not match but its certainly closer than SLOG vs VLOG or Vlog vs FLOG or any other log. 

They've got to differentiate the FX6 and FX9 "somehow". 
Otherwise the FX6 is too good, upsetting many FX9 owners as it steps on their toes. 
At least it still has the BNC TC input! Which is far more important for syncing with the sound department. 
Plus it still has the smart shoe you could use if you really really want to feed audio into the camera while on a gimbal?
That's not a bad thing. 
Yes, for lots of people that is true. If they're casual / hobbyist / indie semi-pro filmmakers. In fact, I'd argue that even cheaper cameras like a a7mk4/X-T4/GH5/E2-M4/P4K/Z6mk2/S5/etc 

But if they're shooting every week with their camera and get paid a fair rate for it, then it is a no brainer to get an FX6 over an a7Smk4! (although, they just might end up getting both)

Watched the gerald undone review of the FX6 this morning.
Kind of confused that 4K Long GOP is only in 8-bit, and you would need to shoot in All-I for 10-bit 4K
Lack of even a 3.5mm mic jack on the body itself means if you take the top handle off to fly on a gimbal, you won't have any audio (except for tiny mic built in to body) is also a bummer. 
Phillip Bloom seemed pretty distraught over the handling.
Dynamic range the same as a7S III???
Seems like for a lot of people the a7S III might be a better fit...

Watched the gerald undone review of the FX6 this morning.
Kind of confused that 4K Long GOP is only in 8-bit, and you would need to shoot in All-I for 10-bit 4K
Lack of even a 3.5mm mic jack on the body itself means if you take the top handle off to fly on a gimbal, you won't have any audio (except for tiny mic built in to body) is also a bummer. 
Phillip Bloom seemed pretty distraught over the handling.
Dynamic range the same as a7S III???
Seems like for a lot of people the a7S III might be a better fit...

It's somewhat less intuitive than the method you mentioned, but one can change the Key Output Gain in the Key window on the color tab.
Just a quick tip: If one uses key frames in the key section of the color tab, you can navigate between them by using the [ and the] keys.