I have a hard drive pre-installed with 16gb of games, just waiting on me building that damn cabinet
- been planning to do it for years.
I think limiting yourself to a single game is a bad idea, you would get quite sick of it before very long, and modern arcade machines just won't hold their value. I say you should look into getting a MAME cabinet, building your own, or looking for an old cabinet that you can refurbish. It depends what type of games you like really, personally I like things like Bubble Bobble and Ghosts n Goblins, so the hardware required is not too expensive.
One concern I'd have with lightgun games is how well they would work, I mean they can be easy to break - it's a big investment to buy a lightgun arcade cabinet then to have it break down would be a right pain - at least with joysticks and buttons you can easily fix any issues yourself.
We're going down... in a spiral to the ground...