Hi,
with most drivers you decide what microstepping you want and apply it by flicking Dip switches on the drive. About 8 or 16 microsteps is about right, that means
that it would take 1600 or 3200 pulses to cause the stepper to rotate one complete revolution.
The pitch of the rack is exactly that, so many teeth per inch or 1.5mm between teeth some such measurement.
If the stepper is hooked direct to the input shaft of the gearbox then don't worry about the belt reduction, you don't have it.
Craig