If you're asking yourself CAN I MAKE THIS the answer is yes!
It's pretty clear l'll never be a film maker or a photographer, but here's a quick video walk through.
Phase 1 - Building the controller
The hardest part of this whole project is building the plywood box, but if you're unable to do that, you can probably scavenge something that will work - an old chest, a toolbox, use your imagination! In this phase, you will build a plywood box, attach a hinge, drill holes in it. At the end of this phase, you will have a really cool, heavy duty, arcade style controller that can be connected to your laptop via USB. Just skip steps 3, 4, 6, 7, and 8
Phase 2 - Adding the Raspberry Pi (AKA RPi)
If you choose to go this route, you will end up with a great controller that just needs power and a monitor (or external projector)- no laptop necessary! Just skip step 4 and 7.
Phase 3 - Add the Projector - this is the finally step to make the whole system self-contained and wireless. The RPi is powered from the projector, and the iPAC is powered off the RPi. Of course the batteries have to be recharged eventually.
1) As with everything, your mileage may vary. I haven't tested all MAME ROMS on the RPi, and I've run into a few that seem to run slow. It could be the ROMS, I'm not sure. If you have specific games you want to play, perhaps try first with just an RPi and a keyboard and see what kind of performance you get.
2) I've been getting about an hour of play time out of a charge, but usually I shut it down after that. I'm not sure what the total play time would be. The projector is rated for two hours, but that doesn't account for the extra drain from the RPi.
3) I've done my best to list all the steps I can think of here, but it's possible I've missed something. If that's the case, I'll do my best to add it once it's pointed out.