Just for variety's sake or to maybe give some inspiration, I used: ochem professor/colleague from my retake of the class, mentor/professor from grad school, former supervisor, organization sponsor for an honor society I was advisor for, and a colleague who worked closely with me every day. I think letters that arent necessarily the "traditional" ones are totally fine too, if you have like a club sponsor, supervisor, coworker, etc that you think could show another aspect of who you are.
The physician letter is probably fine too, if you are concerned you could ask if they think they could write a strong letter / say something like "I was hoping you could speak to x y z (things amcas/ku asks letter writers to consider)" and offer like, your personal statement/a reflection of your time with them/your CV for support. I think the importance is that they are not generic letters. If you feel it will be, 4 is fine!