Really, just the one (I've edited this down since I've learned more about the game) - can anyone help explain the start boost?

Ah yes took me quite a while to figure that one out. It has very little room for error and only works in Time Attack and not in GP as far as I know.

It works by accelerating up to about 5 on the speedometer and the reversing the engine while letting go of the accelerator. The reversing the engine and letting go of the accelerator has to happen at the instant before the third red light flashes on. You can also not go over 5 on the speedometer. Then when the race starts, immediately let go of reverse and press gas.