These are all good points. I did intend to rotate the joysticks to squeeze a tad more room, and even thought of decreasing from 3/4" to 1/2" the wood for the sides and back...every bit will help. I have not mocked this exact config up in cardboard, but will do so this evening once.
I think I'll put in the 4th button in diamond config.
I have a separate panel under the monitor that holds the P1, P2, Start, Pause, and Exit buttons. The reason is this panel will be swappable with others I intend to build later.
Most Excellent!