As a practicing equine massage therapist, the best recommendation I can offer is to get the BEST education possible if you are intending to practice professionally. The Equissage course is a good introduction, but I would highly recommend that you look at schools that mirror the training that human massage therapists get. The practice is more than just learning a few strokes and performing a routine. There is a lot of background learning that is necessary: anatomy/physiology, of course; movement evaluation; human ergonomics; saddle fitting; etc.
Check out the voluntary exam offered by NBCAAM; the course you choose should prepare you to pass this, for instance, and should include hundreds of hours of supervised and independent work on dozens of horses, as well as “externship” hours spent observing massage therapists and other professionals with whom you will work.