1. Building the cab. Is particle board the way to go, or is there any more instresting/funnier alternatives? And ho thick (particle board) would you prefer?
MDF is easier to work with and sturdier. How are you planning to finish the cabinet?
5/8" MDF is a good thickness if you can find it (it's not available in some areas). If you can't get 5/8", 3/4" is preferable to 1/2".
2. Speakers. Is the best place to put them "under the marquee"?
"Best" is in the ear of the beholder, but that's where I've got mine, and AFAIK where most real arcade games put 'em.
3. Coin doors. Do I have any need for a double coin mechanism? Games that really *need* it?
There are games that do need multiple coin mechanisms... Gauntlet immediately springs to mind. I'm not even
aware of any single-slot coin doors. I've got a quad in my cab for those four-player Gauntlet games.
4. Wheels. I've never looked under a cab, but as they are damn heavy there gotta to be some easier-to-move stuff down there? What do you use, nada, or normal "book-shelf-wheels" that make the cabs shaky?
Wheels are a good idea. Get some good sturdy 2 1/2" - 3" casters. Use rigid ones in the back, and swivels with locks on the front. With the front casters locked the cab shouldn't be shaky.
5. The glass in front of the monitor. Plexi or real glass?
Mine is Lexan. Your mileage may vary.