Help with button placement (and additions)

[FutureTrunx]

I have a 2 player layout with 8 buttons for each player and a Utrak trackball (these are already cut on the control panel). The panel also has a spot for 4 other buttons.  I plan on putting "coin buttons" on the front side of the control panel box.

My question is - how should I map these buttons? What other buttons should i set - we also have a spinner that we need to place. Where would be the best place for that?

This control panel was pre-made btw.