>>4058819General purpose, for FF, 50mm f1.8. For APS-C, Sigma 30mm f1.4. You'd get nearly identical results out of either setup. Longer lenses can isolate the subject more, and you can be farther away, but might run into space issues at a con. Wider lenses are better for more "environmental" type portraits. You can get zooms that cover both ends, but you'll lose out on the ability to control depth of field / isolate the subject as much.
a7c does have a relatively small viewfinder (smaller to look through than many APS-C cameras even), but otherwise fine.
The lens will really dictate the types of shots you can get, and how they look (how "zoomed" in/out, lowlight capability, depth of field control, sharpness, etc).
The body will dictate how well you can do that (autofocus, burst shooting, dynamic range, ISO noise, resolution, etc).
Things like lowlight performance and depth of field are affected by both the lens and sensor size.
Not my pic, but XS-10 + 35mm f1.4 to give you an idea. FF + 50 f1.8 would be very similar.
