Missed this up until now. You're doing an excellent job. Couple of things:
+1 on the no beer holders in the CP - that would be a mistake.
the CPR encoder on the Pololu motors is a quadrature encoder, so it is good for measuring actual motor speed v/s requested speed on a robot, but not for positive positioning. There's no way I know of to use it for limit locating in this application. Sounds like DNA Dan has you going for limit switches, that is the better way by far and the controller board is set up to handle them so easily.
Massive cool points for finding and implementing that gilmer belt solution - that will be great. You're rotating a decent sized mass, more than the belt is probably designed for, so make sure you set your start speeds very low via the SMC software, to start out with, so you don't rack the belt over the gear or break the belt teeth off. Then, once you're confident it can handle the start stress, ramp it up. even if you have to start slowly you can accelerate up very quickly to a faster speed if you like.
Again, fine work and you won't regret doing the rotation deal. I still love it every time I play.