Actually, sounds pretty easy and straight foward. I'm getting an encoder, joystick, buttons and the wiring kit from ultimarc... 100 bucks
I found the plans for the midway cabinet that I want on the net. You can use a computer monitor, and run arcadeos with DOS, no need for windows, but you need a soundcard like a Soundblaster 16 or similar that with work with DOS. MAME loves RAM and a good video card (I'm using an old TNT2 with 32 megs and works just nice)
It all pretty much depends of what you want. I saw tons of cabinets with 20 joysticks and 300 buttons to play every single rom. I like vertical shooters and ms pacman, so mine is going to be to play those games.
Read a lot, there's a lot of info in the net. I'm ansy to get this project going, I been messing with MAME since 97, and a cab is a long dream of mine.