First post in here!
@GreekBeast do you live in Greece too? Because this could play a role in buying options.
Your choices depend on a number of things: do you absolutely need AF? Will you often use a gimbal?
1) If you want AF on all lenses, the (Canon) Metabones + Sigma 18-35 is a great choice. There is also the much more economical Viltrox adapter (also for Canon) which has received rave reviews but is backordered almost everywhere. I guess you can expect more than two months to receive it in Greece (due to customs clearance times...)
2) If you go the Nikon way (as I've done) there is the Viltrox NF-43x adapter, which features the same focal reducer as the (AF) Canon version, but is much cheaper, easier to get and of course manual focus only. If you already have a number of Nikon lenses, it surely makes sense to go this way. Again, no AF.
3) I have the Sigma 30mm f1.4. It's a quite nice lens, sharp and with reasonably fast AF. You can usually get this for close to 200€ used in Greece and about 330€ brand new. Haven't tried the 16mm but I'd think the Panaleica 15mm f1.7 would make a better choice; smaller, lighter, probably faster AF. Great for gimbal or handheld work.
In conclusion, IMHO, the most cost effective solution would be to go for the Viltrox for Nikon focal reducer, plus Sigma 18-35mm, plus 2-3 native lenses that cover your most used focal ranges (the Panasonic 42.5mm f1.7 would make another good/cheap option). Because of your low light requirements, native zooms would present some issues. Then add a couple of your adapted Nikon glass and you'll be well served.