Planetary gearboxes

[carl22]

I need to move a 2m long arm (such as a tower crane) parallel to the floor.
I am considering using a NEMA 23 stepper/reducer coupled system with a 100:1 ratio (like the one in the link below) to be connected to the arm with a 3:1 ratio pinion and pulley in order to have a tolerance of about 2 tenths [(1.8/ 100/3)/360*(2*3.14*2000)] I hope the calculation is correct.

Does anyone have experience with this type of gearbox? Is the reported clearance (≤25) measured on the input or output shaft? What is the probability of having a resolution at the end of the arm close to 5 tenths?
Thank you