Hi peteeng,
looks entirely reasonable.

You might be set back a little when you realise the lash of a 5:1 or a 10:1 planetary gearbox.

Most single stage (5:1) Chinese made ones have a lash of 7-8-9-10 min of arc. Two stage (10:1 and higher) about 15 arc min. You would be very disappointed with either.

I had 10:1 planetaries on my steppers, and that was Apex brand and had <2 arc min lash. Chinese 10:1 $100, Apex low lash 10:1 is $450.

May I suggest buy a gearbox, say a 10:1 and try it out. I rather think that you need VERY low lash, and the cheaper Chinese ones may fall short of your expectation.

I found with my trunnion table and fifth axis platter that I needed about 10 arc seconds accuracy/repeatability.....and that is very difficult to achieve with either a planetary
or a worm gear.

Craig