I will definitely mock it up before committing to wood. But I don't understand your concern over the P4 buttons. They're positioned the same as the P3 buttons.
Yes, the buttons are positioned the same relative to the joystick, but the player's upper body is turning in the opposite direction.
For P1 and P2, their shoulders are mostly square to the monitor and the angle of the buttons brings the right elbow out a bit. Good ergonomics.
With P3 standing off to the left side of the CP, their shoulders will tend to turn CCW so they don't have to turn their head as far CCW to get a more square view of the monitor and the CCW angle of the buttons brings the right elbow out a bit. Good ergonomics as long as the angle of the buttons feels natural and doesn't cause P3 to lose track of where the buttons are during gameplay.
With P4 standing off to the right side of the CP, their shoulders will tend to turn CW so they don't have to turn their head as far CW to get a more square view of the monitor and the CCW angle of the buttons
can bring the right elbow out a bit. If it does, that applies CCW pressure to the shoulders. If it doesn't bring their right elbow out, the angle of the buttons can be awkward.
- If P4 buttons 2 and 4 are angled in a CW direction it can bring the right elbow in a bit, applying less CCW pressure to the shoulders.
One other possible consideration is to go with an "angled-square" layout for P3 and P4 buttons like in this image instead of a "smushed-diamond" layout.
- Some people like curved layouts like your current setup. Some people prefer straight layouts like this image. Some might prefer a curved layout for P1/P2 and a straight layout for P3/P4.
- Try several mockups to find which layout or combination of layouts
you prefer.
Scott