Building a small 4th axis

I have been enjoying milling small 3D parts on my Proxxon very much
and have been thinking about making a 4th axis for it.

I have a 4th axis stepper driver so that is no problem but need a
small rotary table. For starters and to learn the process I will
probably try milling some foam or wax mounted with double sided on a
simple plate mounted directly to the stepper motor shaft. I will
only have 400 "degrees" resolution but it will get me going.

Ultimately I want to build a tiny rotary table possibly still without
chuck that will give finer angular resolution. I have some Nema17
and Nema23 steppers that would seem to suit the task on this tiny
mill but no real ideas for the rotary part.

My questions:

1. What sort of angular resolution is recommended for general as well
as perhaps gear cutting processes?
2. How much of an issue is backlash? Can this be avoided by rotating
in one direction only?
3. Is a simple worm gear ok?
4. Are there any gearboxes already available at a low price that will
fit the bill?

I think that's all I need to know but any tips appreciated.

Cheers,

Graham

p.s. My mill is much more quiet now :)