Scaling up in engineering is often tricky indeed. You'd be surprised.
There's operating one motorised fader, then there's the scaling up to 100 of them. The latter is not just the sum of the parts, it's more than that.
You may get power supply issues, timing issues in the microcontroller you have to take into account when writing your code, and even the practical issue of coming up with a wiring scheme that does not make the final product look like a pile of spaghetti (or a breadboard that can't be routed on less than five layers - but which with some rearrangements suddenly barely needs the second layer). Devices may start to interfere in all kinds of unexpected ways. And when you think you got it all under control your sketch has grown too big...
Now reading your further project description, I wonder whether a motorised fader is what you need. You don't need the additional complexity of having to react to and record people making adjustments to your fader settings. This sounds much more like a job for some kind of linear actuator.
To operate hundreds of them is still not too easy, but it's going to be a lot easier than motorised faders - and these actuators have the power (they can get really powerful) and the range (can be seriously long) to push up the liner that forms the surface of your mountain range.