Questions for Blender sculpt artiest.

There is no fixed answer. It depends on the style you want to achieve.

Just remember that 35mm is commonly considered the middle ground. Further below that range would introduce distortion while further above would improve accuracy.

50mm is considered the standard for accurate representation, but you could start experimenting from 30mm and above.

Below 30mm is commnly used for stylized or wide lense style. 24mm is commonly used for indoor architecture.

Ultimately you can use different focal length while in viewport but it is recommended to double check and review things before rendering and that includes the focal length. If it meets the style or camera coverage you want.