Hi
Might I suggest that you ascertain the weight of your proposed OTA, you then need to double it, to account for cameras etc. Then check out the carrying capacities of whatever mount you are looking at, for astrophotograhy you really need a mount with atleast 1/3 more carrying capacity than the combined weight of your equipment, suggestions...maybe a G-11, capacity - 30Kgs, probably not, EG-6, 25Kgs - probably not, Losmandy Titan, yes, 160lbs from memory, cost, well, this is the killer, $10,000 - $11,000, Assen Technolgies, more. As you can see, it starts to get expensive real quick. If you can hold of an old AO GEM, can't remember the name now, you might be able to upgrade the motors. Rings and dovetails, check this site
http://www.parallaxinstruments.com/
Lever arm movement has been mentioned, you need to carry the weight as close to the head as possible, put most of your weight up there and place a lighter one down further for balance, the reason, simply to stop the motors from ocillating when making a correction, the further you have the weight down the shaft, the more it takes to stop a motor and reverse it's direction.
Food for thought.
JohnG