Only one admin button? Is that gonna function as "shift" and your other buttons will do other stuff, or what?
I'm gearing up to rebuild my control panel, but here's what I currently have:
2 8-way and 2 4-way joysticks, which sucks and takes up too much real estate, and will be replaced by Mag-Stik Plus top-switchables...
3" Trackball
Spinner
6 buttons per player, but I will be increasing this to 8 like yours.
Two pushbuttons in the far left corner that are dedicated mouse buttons (the trackball acts as a mouse).
2 coin buttons
2 start buttons
4 admin buttons... escape (exit game/emulator/hyperspin), in-game menu, pause, and enter/select
I probably could have gotten rid of the 4 admin buttons if I used one shift button in combination with the player buttons, but my CP has plenty of real estate and I like the look. Are you planning on using the coin mechs exclusively for "coin in"? I don't have a coin door so I just have a separate button next to the start button that I wail on to add coins. I like the authenticity of the coin doors/mechs but you might want a cheat button somewhere that functions like "coin in" in case you don't have any quarters/tokens handy, or maybe map shift-start to work like a coin in.
Or in a pinch you could map the start button to both the start and coin events, that should work but isn't the most authentic...