I was an infantry CPT when I ETS'd. Got into med school a few months later. In med school, decided to join the Guard. Started as infantry but the time commitment of med school was too much to be able to accept command so switched to med services as a med student. It's virtually impossible to get 4-5 days off completely to certify a team live fire, for example. In med school, you can typically request to get 1-2 days off at a time to go to weddings or whatever but more than that would probably be an issue.
The infantry unit was extremely understanding and I was upfront about the fact that it might not work out but I was willing to try if they were, so ultimately they were supportive of me transferring. I looked into reserves when I looked into transferring as well and they said they don't accept med students, only physicians.
If your mos wasn't medical your time only counts 1/2 towards promotion so I was a 1LT again (not a huge deal). Was told by the Guard med unit I didn't have to go to drill and could just split-train indefinitely. Fast forward 8 months and the new commander told me to get bent and that I had to go to drill. I had already finished my initial 8-year obligation from AD and felt pretty disrespected/disappointed so I resigned (hadn't taken any incentives--was only in the Guard because I liked serving).
If you're looking at the Guard to pay for school, look into voc rehab instead if you have a disability rating. It doesn't draw from your GI Bill so you can subsequently use GI Bill for BAH during residency. If you're looking to serve your community, there are so many options as a physician (or even as a med student) that don't require you to maintain competing priorities. Volunteering at free clinics, doing research, educating med students, mentoring premed students, etc. that will look good on residency applications anyways.
Only do Guard if you are cool with the fact that they could change their mind about anything at any time and deploy you/make you go wherever they want whenever they feel like it. Or if you truly need the health insurance (but schools usually have health insurance for you/your family anyways so not a huge advantage--not sure about gi bill but if you use voc rehab they will pay for this). For me it was like pulling teeth in the Guard to get anything done admin-wise, so consider that as well (it's not like AD where you can just walk to S1 and ask a question to get your pay or whatever else corrected). Just lots of unnecessary stressors during an already-stressful period of your life.
I'm glad I gave it a shot because I would've always wondered, but am even more glad that I got out (again) and hope others will learn from my experience. I mentor quite a few folks going to med school from AD so hmu if you want to talk more