I am currently building my first cab, and also wanted as few extra buttons as possible. I ended up with three admin buttons, and I use player 2 start as the shift button. The default admin controls are - TAB, to bring up the in game adjustments, escape, to exit menus and the current game, and the last one is pause. If you hold player two start and hit the credit button, the purple one, it adds coins for player two. The far left and center black buttons are save and load state when shifted. So far I like this setup and it is pretty user friendly, once you use it a time or two. and it doesn't add too much clutter... Just my .02 cents.