Hi Andrew
I'm sure you'll achieve these design goals more quickly once you see how good the images are with your current system.
I once read a book that suggested there is little difference between a straight and curved drive bolt for the first 20 to 25 mins of a single exposure. After that, the straight bolt needs to be turned a little faster due to the tangent error.
Here is the formula for calculating the distance between the hinge centre and bolt drive for a 1 rpm drive:
D=228.6/tpi
where tpi = threads per inch.
Cheers
Dennis