I am very new to Arduino and this topic
So why have you taken such a huge and complex task as trying to control 100 motorised faders!
Electronics, like many other things does not simply scale up to such large numbers without a lot more engineering skill. Mind you it seems a common thing these days of over ambitious projects tackled by beginners. What tends to happen is they spend a lot of money and give up.
Forget the scaling up until you have the skills to control and understand what is needed for controlling just one, that will be challenging enough.
The biggest problem is making sure they do not hunt, that is buzz when they are still. Then the next problem is to disengage the Motors when you detect a touch on the fader by the operator. This normally involves a capacitive touch sensor on each fader.
Then you have got the things that maybe you have thought of already like reading the position of the slider and moving it to the required spot.their is hardware control of the motor with a h-bridge and the algorithm to move it at such a speed that you don’t get overshoot and yet it doesn’t take forever to get to the right place.
Then their is the analogue electronics in the circuit of what ever the fader is going to control. You have to make sure that the digital noise doesn’t get into those circuits.
It is a complex process controlling just one let alone 100 of the buggers, so please get some skills first before committing to such a large and expensive project.