Specifically, what is wrong with my design? What potential issues could I have, or what should I be wary of?
Is it a little low? Will the marquee block the top part of the screen? Keep in mind I'm 5'11": I'd move the CP (probably eveything) up 4 to 6 inches and the either the marquee back or another ~6" up (for a total of 10"-14").
Again, I'm going on my height, but most arcade cabs have CPs ~38-41" off the ground, AFAIK. And I couldn't stand a lit-up marquee in my face, let alone blocking part of the screen, lit or not lit.
I'm a little unsure of the trackball button locations - is there a more commonly used location, such as above the trackball?
I'd do as shardian said, but map mame so both P1 & P2 buttons work. If you want the "TB buttons" to be mouse buttons in windows or other games, though, some people might get confused without separate mouse buttons.
Anyway, most arcade trackballs were on the left and/or right side of the TB.
Can MAME be compiled with dual core support? Any large performance increases?
Yes it is
compiled that way by default, but you need to "set OSDPROCESSORS=2" ("set OSDPROCESSORS=4" for a quad core, ect) and enable multithreading in mame (-mt at commandline or multithreading 1 in mame.ini) to get the full effect. Even so, most games only get a small increase (2%-10% AFAIK). OTOH, a few games get bigger changes (links below). Having a 64 bit OS and 64 bit mame sees a big change on the slower games, too.
Check this thread and the links to the
mame32 benchmark page.
edit: punctuation, spelling