Question regarding function buttons

[rbbauer00]

I'm repurposing a Konami 4 player cab into a hyperspin.  It will have all the console games plus MAME on it, but it will be mainly used for those games that work on an arcade panel.  I'm going for a 4 player setup with players 1&4 having 4 buttons and 8 way joysticks and players 2&3 having 8 buttons and Ultrastick 360's.  If i can fit it in, I'll add a trackball and spinner, but I realize it's getting kinda tight without rebuilding the CPO box (something I'm entirely capable of but want to keep original cabinet as much as possible).

What I cant decide on and haven't found previous discussion about is which of the "Function Buttons" to add and which to have assigned to a "shifted" button.

I want the interface to be as intuitive as possible for someone who doesn't already know how to use hyperspin, mame, etc.
Gonna try to use the coin return buttons as coin buttons.

I want to use save states and hyperpause, plus an escape/shutdown, enter, etc.

My question is what "function button" layouts are recomended.  Trying to get a balance between functionality and user-friendliness.

[rackoon]

I got a hyperspin set up going on and I have     Pause, enter, escape, volume up, volume down