JDJ
You may be starting a business if you rent the plane and sell your services as an instructor.
I ran into problems a number of years ago when I tried to do what you have in mind. The FBO where I tied my plane down wouldn't let me do it. They had a contract with the airport for doing business off the ramp space they leased from the airport, and I could not subcontract business off their ramp. You couldn't even go out and do anything other than incidental maintenance on your plane on their ramp either, because they had the sole right to do that on their premises, and they were also worried about legal liability, of course.
Depending on the state you are operating in, you may have to collect sales tax on your services and the rental fee you charge for the plane. You may have to incorporate to get a state tax number to use as a company when you collect tax and pay your employees (yourself).
The states take a dim view of you doing business and not paying them their share.
It's not as easy as it should be!!!
As I think somebody said in the thread, it may be easiest to lease the plane to somebody who already has an established business.
TriDriver Bob