Greg,
There is no need for special motors, standard NEMA17 (preferably 400step/rev) is widely used.
To achieve the required rot. rate and smooth movement for EQ platform, people are using various methods..
For example, threaded bolts and driven nut, shown on
this website.
Or,
here author used two bent threaded rods (lower on page) as worm wheel sector and third one (with same pitch) as worm, coupled with stepper motor directly or via suitable reduction (up to 1:2 is adequate).
The whole thing can be controlled with OnStep (or equivalent) electronics.
I wish you luck :-)
And you can always ask the question here, there will be plenty of help available from members of this forum.
Edit: first you have to calculate the required reduction. As a rule of thumb, aim for 0.2 arcsec/step.