Greetings Christian,
If your still around, i'm in the process to building out my BMCPC rig with a arduino minded pot (maybe a different hand control... i'm found a few comfy alts) controlled duel servo system. One servo for Focus, the other for zoom (depending of the glass obviously). I have several answers to many of your questions, but i'm not going to burn the time typing it all out unless your have yet to achieve your goal, and if you have perhaps we could compare notes.