My input. Totally subjective of course.
1. Use an RPi. Along with a good premade image, it's pretty much plug and play.
2. For a general purpose cab, go for 2 sticks, 6 buttons per player. Use an iPac2 for control interfacing.
3. Using some usb exention cables or whatever, make a few USB sockets available at the front of the cab, for plugging in keyboard, other controllers etc
4. For sound, the easiest thing is to cannibalise some PC speakers. With some simple soldering/wiring, you get an amp, psu, speakers and a muting headphone jack.
5. Use a CRT.
6. Use a CRT
7. If you don't use a CRT, at least use a sensibly sized 4:3 screen. Resist the temptation of a big screen. 19-25" is best, and I prefer sctreens at the lower end of that range. When the screen gets too big, it makes games hard to play. You are standing right up close to it, and you won't be able to see it all at once. A screen that natively does something like 1600x1200 or 1280x960 would be ok. Combined with a the CRT shader in retorpie, it will look ok.
8. But use a CRT, really. Standard VGA CRT monitors with a wide range of horizontal scan rates are great as you can feed them integer scaled versions of almost almost any native arcade resolution and refersh rate.