Timing Pulleys for CNC Work - OK or Not ???

I have been a lurker here for some time but now is the time to get
more
active as I have some CNC projects to work on.

I am presently working on my first CNC adaption on a SB lathe. I
plan
to use steppers with a gear train to provide finer control and more
torque with less expensive steppers. I know that many designs just
attach a 200 step stepper directly to the lead screws, but I believe
this approach will be better and perhaps not cost a lot more in
materials.

Anyway, my question is about the connection of the final shaft of the
gear train to the lead screw. I would like to avoid an exposed gear
(the main gear train can be enclosed) so I was wondering about using
a
pair of same size timing pulleys to transmit the motion. I know that
the belts are reinforced and do not appear to stretch much but are
they
really suitable for this kind of service? What kind of errors could
I
expect from such a linkage? Does anyone here have any experience
with
then in CNC work? If suitable, how would I calculate the pulley size
to use based on the expected torque? Or what should I base the size
on?