I have built 3-4 MAME cabs and also 3-4 Multicades. You really need to ask yourself what games you (and your family/guests) will actually be playing. In my situation I have found that 95% of the time it is the early 80's vertical classics. (Pacman, DK, Galaga and the like) In that case, I really belive a Jamma card put into a previously gutted cab with a 19 or 20 inch 4:3 (actually 5:4) is the quickest and most cost effective way to go. Cabs and monitors can be found on Craigslist all the time. And there are many other places to look
Is the emulation as good as MAME, not even close. Can you change the gamelist and frontend look...not really... But to get up and running with the classics...its pretty slick.
That being said, I have 6 cabs in my house. One with a 60-1 / 412-1 with a jamma switcher, one an ArcadeSD, 2 dedicated and two MAME cabs. By FAR the ArcadeSD cab gets the most play.
I completely enjoyed building the cabs and learning MAME, Hyperspin, Mala, etc... Very glad I did. I also had fun with the woodwork, painting, artwork, etc...
OK...so kind of went off tangent there, sorry... Button colors...whatever you like. Layout depends on games you want. Best advice already given is dont try to jam too much on the cp....just gets to cramped and busy.
Full computer....admittedly dont know much about the Pi...but some stuff is pretty cool. RaspberryJamma looks pretty neat.
Good luck!