Not really sure how to calc with pulley and belt but heres what I think.

If you have 200 steps per rev of the motor and 16 micro steps that is 3,200 steps per rev of the motor.

You have a pitch of 2.032mm and one rev moves 20 teeth so thats 20 x 2.032 =40.64mm per rev

Steps per mm will be 3,200/40.6 = 78.74015748031496062992125984252 steps per mm.

Hood