Yeah, I'm going to agree with the resist the frankenpanel instinct. I was originally not even going to have that big of a control panel, 2 super 8-ways, a 4-way pacman reunion, plus a happs trackball, and a spinner. Having extra parts is always nice, but I now have bout 2 boxes full of crap from various projects and my original cab. I believe I have 2 trackballs, a 4-way off-brand yellow balltop, a 4-way pacman reunion, many pushbuttons, a 12v trackball light adapter *definitely didn't need that one*, and after I finish my 2 solo joysticks and my versus cab, a box full of left over competition pushbuttons plus 2 psx pads.
Things I have learned from my experiences:
drawing power from a usb mouse on an imperial trackball if you do it wrong will blow out the usb port *sorry dad*
never use the "ship the items as they come" from happs, they charge you for every shipping they do.
Never buy off of ebay without checking for a name or brand, if there isn't one it's more likely than not crap.
Always cut less before you cut more, you can take off more than you can put back.
Always overestimate your projects, my mame arcade is still sitting without a tv and a new pc, its only running on hand-me-downs and the control panel.
NEVER use X-Arcade parts, they might work fine but they won't feel as nice as happs parts.
Do take advantage of fixed shipping charges on ebay, I scored 40 buttons or so off of ebay w/ $3.50 for shipping, the price on the box said $12.50 for shipping.
New happs trackballs spin better than any old trackballs I have ever tried, my happs spins around 13-15 times with a moderate swipe, my wico and imperial are limited to bout 4-5 spins, even with a new bearing set.