Blake I'll get the ball rolling with my take on this. I'm not talking from a great spread of practical experience but am working on something in the shed.
- Servo's are reported as better then steppers. I've not yet used servo's but from what I've read steppers mostly win on price (motor and controller).
- Direct Drive seems to be very cutting edge. I suspect that for most mortals a well controlled motor and lot's of reduction is where we end up.
- Worm gears provide a lot of reduction in one step with limited backlash. They also provide some holding capacity (they don't run backwards under load). Kinetic (Steve) has done some great work on home made worm gears and given some great info about it on other threads.
- Over to others, I like aluminium because it's light, easy to machine and does not rust. Stainless shafts make a lot of sense.
- I've not seen anything on fitting manufacturers go-to tracking on home built EQ mounts. Mel Bartels servo drive system might be useful
http://www.bbastrodesigns.com/BBAstroDesigns.html The Argo Navis
http://www.wildcard-innovations.com.au/ can be fitted to a wide variety of scopes and if you are building one allowing for encoders should be a given. It can interface with the Servo Cat (and some other drive systems).
- I suspect that will depend on what you hope to achieve and what skill's budget and equipment you have. You could throw a lot of money at a home built mount and never get the result's you want but if you have the skills and equipment then you might get something that's hard to buy both in hardware and satisfaction.
Bob