As someone that's built a bunch of DOS based cabinets, let me toss in my .02
First: forget booting from a floppy. Yes, you can get 1.44M of info on one, but it's just torture. eBay regularly has small drives for sale for extra, super cheap. Most normally because someone just wants them out of their house. I'm using a 200M drive on my Galaxian conversion, and I think I'm using *maybe* 20M of it. And that's with a bunch of extras that I just tossed on there.
I
just bought this to play with. Boot time should be minimal, don't need a hard drive, silent operation, and storage is the amount I choose.
You didn't mention what kind of monitor you want to use, but I suggest a real arcade monitor. Depending on your locale, you can find one from free to just a few bucks. Might need a little work, but this *is* a project, right?
To save a bunch of woodworking, you can probably find a converted Pac-Man, Ms Pac-Man, Galaxian or Galaga cabinet that's empty or just has some POS game in it for cheap. That's how I got mine.
And finally, for booting into a single game, it's as easy as this: at the end of your autoexec.bat...
cd \mame103
dmame pacman