There is really not much you can put down on paper when recruiting independent contractors. The most important part for them to sign before coming aboard is the non-solicitation agreement. Beyond that you can add their duties requirements/assignments, working hours (schedule), payment schedule, the type of uniforms (if any) they will be required to wear while working at your location, rules of conducts with your clients/members, termination policy and also a list of the certifications and insurance which they are required have.
Maybe someone else here can provide you with some extra information and advice. I hope this helps.
I would consult an attorney. It may cost you a little bit of money. But if you don’t get it right and something goes wrong, it could cost you a lot of money. You could also consult other wellness centers in your area. They may have a contract that you could use as a template and insert your information into for an attorney to go over for you. Contracts are not trivial matters.