Hello and welcome to the forums.
As already said, I would fix those player 3 & 4 sticks so that they are not angled.
You want up to be up just like player 1 & 2. If you wanna read more on that, just search the forum. It has been discussed to death (and then on some more)
That's a nice looking cabinet. Looks like it'll make a great Mame machine.
In order to do your 4-player panel, you would build the whole control panel as its own box (remember to slightly angle the top panel down toward the player) and notch out the front area of the cabinet like a shelf in order to mount the control panel on it.
You can add some 2x4 pieces in the shelf and screw the panel to that.
I've attached a pic of a TMNT cab (not mine) to give you an idea of how the cabinet looks without the control panel so you get a better idea.