[575] How is the bit-resolution on the PWM output for the spindle control? (8-bit or higher?)

I am not sure of the resolution for the PWM output for spindle speed control. However, if you are worried about getting the exact speed you need, 8-bit will provide 256 levels of increments. This translates roughly to a change of 94 RPM from one increment to another. Remember to provide some inductance and shielding to the signal lines so you won't get fluctuations in speed.