My brother in CA has this permit and MI (where I live) just recently passed it. Personally I do not partake, even though I qualify, for many reasons and especially since the Feds (FBI, ATF, etc.) can still bust your ass and lock you up - just give them half an excuse. Of course, local, deputies and troopers cannot touch you for it. If you hunt, own handguns or enjoy shooting sports, you may have your firearms confiscated, or, not be allowed to purchase new ones...ask a lawyer familiar with Federal Law first.
As for the doctor, it is my understanding that if you qualify, you cannot be turned down. If one refuses, try another and ask your friends. TN law may be different than MI. Again, ask that lawyer (above) and/or your state's website for the correct procedure.
Getting the medicine may or may not be a problem. Don't try growing outside, use a registered "care giver" and don't go over any legal limits! Know them beforehand.
Hope this helps.
Ted