Hmm.. maybe a bit slimmer? (from front to back). I built a "slim" built and boy is it big. You don't realize how big these things are until you build them. Also, if you're concerned about the weight on the front, they do sell weights you can attach near the back (on the inside of the cab) that will help it be stable.
Also for player 3 and 4, I don't think you need that many buttons. I've never seen more than 4. Maybe you can use the extra buttons as pinball buttons?
Have you decided on a button layout yet? Maybe you can do a cardboard one or draw one out on paper to see how the spacing and amount of buttons feels. From looking on these forums, it seems like the cabs with less things look nicer. If I had to redesign my control panel.. (I have only player 1 and 2; 7 buttons each player) I probably would have taken out the trackball and spinner. I have some topguns that I'm considering selling because the sensor bars are making mounting the monitor more difficult. I Know you haven't mentioned any of this, just sharing it in case you're considering any of this. In the end it's your preference and whatever works for you. Nice choice on colors, but why is one of your blue buttons darker?
Are you sure you don't need more quick connects? I used one pack of 100 on wiring half the buttons and joysticks that you have. Then again, I had throw away a bunch due to mistakes.