Hi Lars,
I am happy I was able to help :-)
As to 16-teeth pulley, it is standard (for 3D printers) and that is why it is low cost. If you intend to use 400s/r stepper and OnSTEP (or similar) with ustepping Pololu module (32 usteps), you will have 0.15 arcsec resolution (100Hz stepping rate for tracking) - more than enough (I have 0.225 arcsec, and no tracking problems with 1000mm FL AP & visual).
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