1) Try out wiring.
2) Not build the entire cabinet.
3) Try out a Raspberry Pi.
4) Keep things cheap.
As mentioned there are a lot of great resources out there for this kind of thing. www.PiPlay.org was a great location for the software for the PI and www.instructables.com had several good posts with the necessary steps.
This whole project took about three weeks of evenings from planning start to completion so it really doesn't take a lot of time to get something functional. So far I've managed to install Super Mario Brothers which was my favourite game as a kid. Now I don't have to share with my brothers.