My DH is a certified massage therapist. He took classes for about 8 months I believe. He only does it as a part time thing right now, but yes, it is hard on the therapist's body.
The pay all depends on what you wish to do. He's in with some others at a massage clinic, they can work 8-10 hours a day or just a few. He pays a small rent when he uses one of the rooms. Other places have told him they provide clients, he shows up, and they split the money 50/50. Then there's always the option of opening your own clinic, but it can get pricey.
You must also allow time for continuing education, and have to have a certain # of hours in our state (Va.) to renew the license each year. Plus you need a table (or 2) and the creams, hot stones, etc. Most places he's thought of working require you bring all of your own things.
Good luck!