How do I choose the right NEMA 17 motor for an electric focuser?

Hi everyone, I’m planning to build an electric focuser using a NEMA 17 stepper motor from www.skysmotor.co.uk . I have a few questions regarding the selection process and would appreciate your advice:
1. What is the ideal holding torque for a focuser? Is around 40 N·cm sufficient, or is a higher torque recommended?
2. Is it necessary to choose a NEMA 17 motor with a gearbox, or can microstepping the driver meet the precision requirements?
3. Is there a significant difference in actual focusing precision between 1.8° and 0.9° step angles?
4. How can I minimize the impact of vibration and resonance on image quality during low-speed operation?
5. Are there any specific recommendations regarding motor current and heat dissipation for astrophotography applications (involving low temperatures and long operating times)?
I’d love to hear from anyone with hands-on experience—please feel free to share your model choices and any lessons learned from past pitfalls. Thanks a lot!