How to Choose the Right NEMA 17 Motor for an Electric Focuser?

Hello everyone, I plan to build an electric focuser using a NEMA 17 stepper motor from skysmotor.co.uk. I have some questions during the selection process and would like to ask for your advice:

1. What is a suitable holding torque for a focuser? Is around 40 N·cm sufficient, or is a higher recommended?

2. Is it necessary to choose a NEMA 17 with a gearbox, or can microstepping drive meet the accuracy requirements?

3. Is there a significant difference in focusing accuracy between a step angle of 1.8° and 0.9°?

4. How can I reduce the impact of vibration and resonance on image quality when operating at low speeds?

5. Are there any special recommendations regarding motor current and heat dissipation in astrophotography environments (low temperature, long-term operation)?

I welcome experienced builders to share their model selections and troubleshooting experiences. Thank you very much!