Yeah, P3 & P4 joystick angle....the eternal mistake.
Look at the bolts and "up" arrows on real 4 player arcade panels.
(gauntlet, gauntlet legends, nfl blitz, nba showtime, the simpsons).
We need to make a "do not angle P3 and P4 joysticks, here's what we mean and why" thread that we can just link to every time.
Half the time, people don't get what we're talking about and think the buttons or player position would change.
I don't agree with the people that say you'll never use a 4 player panel.
Build what you want (except for angling the sticks!).
I wouldn't let the additional controls affect the placement of P1 and P2 controls though.
IMO, having it look balanced for 4 players isn't worth being crammed together for 2 player fighting games, which will probably be played much more often. Looks like you have plenty of elbow room.
EDIT: You might consider a 4/8 way switching joysticks instead of a separate stick.