I agree with the comment to dispense with the dedicated 4-way stick. In this era of Ultimarc T-Stik Plus switchable 4/8 ways, there's really not much reason to include one.
I really don't think you'd have a problem with your spinner where it is, despite what others have said. Your arm won't be coming into the spinner from a directly 180 heading. It's gonna come in at an angle from the left, which would allow it to reach around the joystick.
If I wanted to stick close to your layout, I'd probably move the trackball over to where the 4-way is now. Put 3 buttons in between the spinner & TB (Missle Command). I'd probably angle the P3 & P4 groupings a bit more so that each player has a bit more standing room. (In fact, I
did.

)
http://www.arcadecontrols.org/yabbse/index.php?board=10;action=display;threadid=23028If you line the sticks up horizontally, you're gonna end up with an even wider panel. If that's not a problem, good. Personally, I think that the panels that are twice as wide as the cabinet look
aweful. I've found that you can comfortably play 2-player Smash TV and whatnot on a panel with sticks that aren't even. Your body and mind adapt fine.
For aesthetic and funtional purposes, I'd place all of your control buttons in the top middle of the panel. Easier for any player to reach all buttons that way.
After alot of reasearch (there've been several threads discussing this), I went with a similar but different 7-button layout than you have planned. I used:
1234
456
Any other layout will require some reprogramming of the buttons within games. If you're gonna use your lowest left button as B1 and continue the Neo-Geo layout across the bottom you'll hafta reprogram all the Street Fighter layouts. Not necessarily a problem, but something to think about none-the-less.
Here's a
VERY useful tip. Go to your local office supply or art store and buy a piece of foamboard. Cut out your CP shape and controls (SHARP razor blade). You can then move stuff around to your hearts content. Place it at the level and angle you're planning on mounting the CP. Pretend you're playing games (make sure there are no witnesses). Get some friends to stand next to you and make sure you have room to move. I've got foamboard representations of most control types available which comes in very handy every time I design a panel for a cab I'm building. Here's about the only pic I have though.

Note that this layout was completely rejected.

The trackball is basically unuseable by anyone who wishes to spin it with their right hand. Here the P2 stick DOES get in the way. Remember folks, your arm has a left to right or right to left angle when reaching for the controls.