>>3778523pictuers on ig, biggest photographic platform right now are like 1080p, so 2mpix. So yeah, it will be good enough. You will have less room for crop though, so keep that in mind.
Early gen sony a7 have some problems with focus peaking, when it shows everything is in focus. IDK if a7s also has that problem you have to check it out for yourself.
About other option, don't discount crop. Corner image quality is universal issue of all vintage glass. Almost every lens will be noticeably softer in corners wide open, but vintage wide angle wide open is probably most unholy combination of all. So when using crop you arent exactly loosing much.
I used to shoot 5d classic, and it was terrible for vintage glass, because no live view and flawed light metering when using glass without contact pins. Then I moved to fuji xt20. I can't say I miss full frame all that much. Xt1, xt2... etc line has some cool stuff for manual focus lenses. Pic related. Big window is full field of view, and small window is 5x magnification. I think this is amazing, especially when peaking doesnt work like with macrophotography.
And honestly, don't discount canon EOS. Some of most interetsing vintage glass is M42. Yeah canon FD is nice, minolta md is nice, konca hexar is nice, olympus OM is nice, but when you quickly realize after investing in 6 different systems, adapters cost quickly add up, lol. Especially if you want to go for some of cooler adapters like adapter with drop in ND filter, close focus with helicod or tilt shift. If I'd have to invest in only one vintage system, it would be M42, because it has more than jupiters and helios. Takumars and carl zeiss jena are really cool glass.
