If you use the AD7147 chip to detect the touch, you don't have to periodically read in your Arduino loop.
The chip can set an Arduino interrupt when anything is touched or released. (page 29)
It handles 13 touch contacts so you would need 2 of them.
So here's my easy, use-prebuilt chips approach.
2 AD7147 chips for the touch control.
3 ADS8028 chips to read the fader voltages
3 AD7808 chips to provide the output control voltages
24 MC33030 chips to control the fader motors.
All the AD chips have built-in shift registers; couldn't ask for better. Only 2 dig pins needed to shift data in or out.
Since the shift registers can chain, you might need to use up only 6 digital pins total.
The MC33030 chips provide noiseless bi-directional non-pulsed control and output driver circuits for the fader motors.
I don't know what your budget is but, to my thinking, these chips do all the hard part and do it very well.
How much do the faders themselves cost?
With these chips your software is much much simpler, and you can focus on the more fun, user interface part.