Thanks, you've all been enormously helpful! I should be all set now.
If you like, I can post pictures of the whole setup in action in a day or so.
Please do! 
My arcade cabinet, converted from an old touchscreen machine. It runs Windows 7 on a second generation intel i5 PC with 8GB of RAM. More than fast enough for most emulators.
The TARDIS design was my wife's idea, and I really like the notion of an arcade cabinet being a "time machine" that takes you back to your past.
MaLa isn't a very elegant frontend, but it's useful and very customizable. I like it.
Each emulator's game selection menu is hand-crafted to evoke the feeling of the machine it emulates. I add screenshots and control instructions for each game.
Control instructions for Metal Gear 2. (I use an 4:3 19" LCD monitor, but also a scanline generator to get a hint of that lovely CRT effect.)
And there you have it. The little penguin and I are off to explore strange new worlds.
Thanks again to everyone who gave me such prompt and helpful replies.
You guys are amazing, I couldn't have done it without you!