Some preliminary points:
the adaptive vsync issue Ross discovered really seems like it could be very well behavior baked into Wine itself. It'd be prudent to test and determine this as soon as possible, possibly by contacting Wine devs and try to get a patch for Wine made that addresses it.
I think we should try to categorize all the games we'll be dealing with, because different types of games will require slightly different approaches depending on the graphics API used and other various nuances in the implementation. I imagine we'll have to tackle a lot of games on a case to case basis so it's important that solutions found in such manner will be correctly classified so they can be reused for others. Like for example as Ross mentions, some games actually benefit from going the whole dgvoodoo + DXVK route but a lot probably wouldn't.
Regarding the 4:3 thing, I suspect using Proton would be best since it has fullscreen scaling built in, unless vanilla Wine has finally got that upstreamed. Assuming there isn't a game-specific patch on http://www.wsgf.org/ of course.
I do think Lutris should be used as the "base of operations" because it has the best per-game configuration options, including an option of easily enabling DXVK. The only thing it misses is an easy way to make prefixes, but it's not like it's hard to make prefixes, even from a terminal.
I'll write more when I have time and as I collect my thoughts.
Edit: also I see nothing wrong with your checklist so far btw, Ross, seems like a reasonable starting point