MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
There are many possibilities for homing switches and they all have pros and cons. The inductive proximity sensors are quite adequate for this application (and given a stable ambient temperature they are quite repeatable). They don't require additional electronics, are easy to find and cheap (I've seen them for as low as $2).
A planetary gearbox would have the advantage of being smaller in size, however, it is just as backdrivable as the simple gear if it uses the same transmission ratio. It is true that if the power is lost, a heavy camera that is mounted unbalanced, will sag down. This is helped somewhat by the back-emf of the motor (think electric braking). In any case, the best performance is achieved by mounting the camera so it is in balance. Once the pivot point is in the desired location relative to the film plane I suggest to use weights to balance the axis. That way you get the same torque to work with tilting up and down.