I am hoping to begin work on my control panel this week and have been doing a lot of reading and research.  I have updated my control panel layout to reflect the curved button layout that I am going with.  I also realized that I needed to move the trackball up some to allow room for the control panel hinge.  
The big thing I have done is decide to put the spinners on the outsides.  Player 1 (left side) was already there, but I originally had the Player 2 (right side) spinner next to the track ball.  I decided to move it to the outside.  I think this makes it look a little cleaner and more uniform.  The spinners/mini wheels are represented in the picture by the button with the big blue circle around it.  This is the 5" mini wheel that I want to use.  I think there is plenty of clearance now on both sides.  I even have a little more room to move them out further if I need to for clearance.
This layout gives lots of options as far as number of games that I can play.  The normal games with 1 or 2 players with up to 7 buttons each.  Trackball games, spinner games, racing games with the mini wheels and buttons.  I also can play single player 2 joystick games.  As well as some specialty configurations by using a combination of Player 1 and Player 2 joystick and buttons for games like Defender, Stargate, Asteroids, etc.     
Please let me know what you think and if you have any thoughts or suggestions.
P.S. the joysticks show as 8 way, but I will be using U360's for maximum options (2 way, 4 way, 8 way, diagonal, analog, etc.)