Since this is a 32" Cabinet, Could I make it a 4 Player? I would like to play TMNT, NBA Jam, and Gauntlet...
You can do anything you like, just don't angle the player 3 and 4 joysticks.
The player can stand at an angle and the buttons can be on an angle, but the joystick orientation should be parallel with the first two players.

This hasn't been done many times, but if you put them all in a straight line you can play the dual joystick games like smash TV.
As far as appearance goes, I think they look better offset.

It might get tight with a trackball in there.
No games in MAME use more than 4 buttons for players 3 and 4. And only two games use 4, the two Dungeons & Dragons games.
The rest in MAME only use 3.
So if you don't plan on emulating 4 player console games, there's no point in having more than 4 buttons for those players.
Personally I'd only do 3 and then map a combo for the D&D games.
Looks good so far.
Your woodworking puts mine to shame.