- how do I add grain?
Simply by >effects >stylize >film grain >realistic grain (as opposed to iMovie grain) >amount between 5 - 12%.
BTW & OT: With Motion 5 as a developer tool for FCP X effects, much more could be rigged. So for example the complex filters of the 'Film Convert' plugin. It takes into account that analog color film stock is composed of three layers of colors (not channels) resp. layers of colored grain, magenta, cyan and yellow, with different characteristics, depending on the emulsions speed, and that the three layers have a slightly different focus. My opinion is, that mimicking a certain film stock is useless though, because we live in a digital world, and we only fine-tune a look with such filters.
- how do I export as ProRes master
You make the project setting ProRes or ProResHQ, then you export as 'original'. Or specifically ProRes (Compressor preset, since 10.6 to be saved in the share menu).
- and encode this precisly to x264. Sorry for being a bit lazy, I haven't got time and access opportunity to try it out with FCP-X right now.
I think the best way is to install the free MpegStreamclip, download the free X264 QT-encoder-component (I use this one). You open the master with MpegStreamclip, then you export as mp4 and choose 'X264 encoder'.
If you downscale 1080 to 720 for vimeo, check 'better downscaling' in MSC, avoids scaling artifacts (moire!
My suggestion is to create a preset for only the clips that were shot at the same time. If you shot 10 clips within 15 minutes the lighting will not have changed that much to cause a difference ...
, if you film on a grey day. But with the sun as a light source, everything can change dramatically within minutes. Or if you change the camera position.