I like the colors in your design. I'd also suggested lighted buttons to pimp that up! Since you are getting a TT2 from GGG, consider getting their Novagems. I have them and they look great. With your artwork, I can only imagine how great it will look.

You will also probably get feedback about the wheel being below the trackball. If you are playing Golden Tee or any game where you need to spin the trackball with any velocity, that wheel will be in the way. IF possible, slap them in some spare wood or sturdy cardboard and try it out. You don't even need to hook them up.
Or, if you go with the TT2, leave the wheel off most of the time and that will help some. But I don't think it will be very easy or comfortable to use. My two cents.