I would join an organization like the American Art Therapy Association and email/talk to actual art therapists and learn how in demand it actually is and how to shape what you are doing now so it will work in 4-5 years toward something like you envision.

One thing that caught my attention with your vision was that there wasn't much indication of the hard work and the boring stuff that is in there too? It is not all learning, art and fun? There is paperwork and practice and the day-to-day stuff that goes with doing anything at all, even stuff we love. I am a research historian and writer but I have to do timelines which I hate, the fiddling with the exact dates and putting them in order and getting the bare facts down, etc., why many people "hate" history and think that is all there is. Well, to an historian, it's other stuff that is exciting but every single job/career/calling, whatever, has its boring or difficult staff meetings, etc. Of course, the "public" does not hear about those because that would be like talking about going to the bathroom in a novel? LOL No action or glory there.

Yes, you may need graduate school but that just becomes part of your life and how you get from here-to-there, where you want to go. We never "arrive". You don't find something you enjoy doing and then are set for ever and every, happily ever after. Life keeps moving, basically like it is doing now and what you do and want to do keeps changing (think of technology and how much it has changed since you were a teenager/the last 10 years?).