Should the students help clean-up?

YES! This is an important part of their learning responsibility. However, you should be the one to return the equipment to storage.

How should I leave our practice space?

It should be in the same condition or better than you found it and ready for use by the school.

When should I put all of the equipment back to storage and return the practice area to the condition it was before class?

AFTER you've returned the students to their class.