I went through a lot of the same questions you are asking now, so I can relate.
After much debate (between forum members) I ended up going with joysticks that are directly parallel (or perpendicular depending on your view point) with the display. Basically, no angles for the joysticks even though the buttons are at an angle.
You may want to straighten out the PL1 and PL2 controls if possible. These will be the ones you use the most, and it would seem a little odd to be at a slight angle all of the time.
Unless you are doing console (PStation, Nintendo, etc) emulation, you may want to drop the 5th and 6th buttons for player 3 and player 4. I was going to have 7 (yes 7) buttons for all 4 players, but dropped them all back to 6 (I liked the uniform look of things) and then got practical and dropped PL3 and PL4 to 4 buttons. It gave me more room on the CP too, and I really like the end result. I also realized that I would not be doing console emulation, so that helped with my decision. I learned from my first cabinet that you can spend a LOT of time or a little time on tinkering and tweaking. Myself, when I get MAME, Daphne, and Pinmame running, I am stopping and enjoying it. I have an overkill PC for most arcade games (AMD Athlon XP 2900+ with 512MB PC3200 RAM), but should I ever want to do something different down the road, I will have a little more horsepower than my old setup with a Pentium III - 500Mhz.
As for your design. I almost built a similar unit at one time with a pedistal and then a projector. The problems were as follows:
1) Getting the room dark enough to really enjoy the large projected display without making the room unusable.
2) Getting the room dark enough, and still being able to see the control panel (backlit buttons and so forth would help with this, but wasn't an option back in 1999)
3) Most important problem, my projector died about 2 months before I was going to start building, and I didn't want to spend the money on a new one for another arcade cabinet since my first cabinet was still 100% functional.
Now that I am finally back to building my second cabinet, I went with a 27" TV like the first time, but upgraded the quality of parts and construction to make a professional looking cabinet. For me, that is more important because I need to consider the WAF (Wife Approval Factor).
Update your design a little, repost it, and let us take a look.