I actually ordered the exact same panel (it shipped yesterday). I'm not using coin insert buttons (they will be replaced by blank "caps" just to fill in the holes), in order to force the user to insert tokens at the coin door, so here is how mine is laid out:
CAP -- P1 START -- PAUSE -- CAP -- P2 START -- TAB -- ENTER -- ESCAPE -- SERVICE (F2) -- P3 START -- CAP -- PAUSE -- P4 START -- CAP
I've discovered that selecting options in the TAB menu required pressing the ENTER key, so I used a dedicated button there.
I'll probably cap the 4 buttons around the spinner, since I have no problem using the P1 or P2 buttons, even though they're a little low for spinner use.
Onyx