I built one last summer.

From my experience, you will need a GeForce 460 or better and 3.0 Core2Duo or better. Go SSD, 128GB should be plenty. Windows 7. 8GB RAM. I love mine. Everyone that comes over enjoys it as well. There is a slight lag, but you get used to it quick. It is what made me start getting real pinball machines. Be careful!

I am running PinballX. Very easy to set up. Going that small will be cramped but I actually plan to do the same, a table top, just because.

What exactly is your question regarding the build?

I used a Kade emulator for the buttons. you can use an iPac or any keyboard encoder really. I used leaf switches and pinball buttons in mine. but arcade buttons will work fine also.

I do not have that issue with the DMD. Maybe not as bright as a pinball DMD, but it is pretty bright. Definitely not something I noticed. I am running 3 monitors. What set up do you have for the display? Which Pinmame are you running? 2.5, right? VP 99x?