Status: Completed mostly. Decided not to worry about joystick commands, since they should be easily changed.
Stage 2: get the Pi to automatically boot into mame with some sort of game selection screen that can use the joystick instead of a keyboard
Stage 3: Get Ms Pacman to flip like a classic arcade cocktail table depending on if player 1 or player 2 is playing
Stage 4: Wire a joystick(2 if possible) and buttons to the GPIO pins on the Pi.
Stage 5: Come up with a plan to power everything so that only one cord is required if possible
Stage 6: Design and make the box
I'm likely putting this project on hold until I can purchase joysticks/buttons/ipac2 etc. I may make a project 2b that involves making a console emulator which will require a lower budget.