Yeah the handset is nearing completion, the motor is what needs doing next.
Im also slightly worried about voltage and signal loss over longer XLR cables. I am thinking of putting an encoding system in so there is a decoder at the other end. It basically fires a higher voltage down the cable so the voltage loss isn't as damaging and the signal is sent digitally then decoded at the other end. Less likely to get interference aswell. The decoder will be a little box with a plug on it. Might have a 9v battery inside it. Impact on final cost fairly minimal.
Kind of taught myself. I learnt a lot from making the remote p/t camera head and the video transmitter. Its a shame its easier to transmit video than it is to transmit servo signal.
To replace the XLR if you were trying to go with something more compact. Probably cost more though and sizes/pin arrangements are somewhat difficult to find.