QUESTIONS:- What kind of medical practitioner should I get to examine, and if necessary treat, these problems with my right hand/wrist/arm? General practitioner, physiotherapist, physical therapist, chiropractor, osteopath, hand surgeon, occupational therapist, physiatrist, massage therapist, neurologist, Hellerwork practitioner, ... ??
- What are the best ways of eliminating all of the remaining tension and discomfort in my right hand, wrist, and arm?- What are the best ways of eliminating all unnecessary tension when playing the piano?
From reading your post it sounds like you have issues being tense in your right thumb. Any tension in the fingers or hand will often create tension all the way up the arm, shoulder, back etc. If you feel your right thumb with your left hand, is it stiff while you play? Does it resist any external force trying to move it around while holding down the key? Often pianists tense it even while not using it.
How's your wrist, can you move it around - up and down, left and right, move it in circles - with ease while holding down any key with any finger? If not, this is a good skill to start working on. It practically demands relaxation in every part of the playing mechanism, from fingers, hand, forearm, shoulder etc etc.