When I tried to recruit Gar as a follower, he turned me down, saying that I was "a bit inexperienced for me to put my life in your hands." Is there a minimum level requirement like there is with Magnus? (I also read that you can gain a fate point by setting him free, but I'm not given the option to do that, even after I intimated Parnell into handing Gar over to me. Do you have to add him to your party first?)

You need 8+ Intelligence and two ranks in Persuasion (which also requires 9 Charisma) before you talk to Gar. Once you do, bring up the topic of green tea, and his facade will slip. You will then have the option to ask him to join your party, and then you can intimidate Parnell into relinquishing his claim.

Then you can speak with him again, and either ask him to join, or tell him he's free (and you gain a Fate point). You cannot get him to join you otherwise, no matter how high your Charisma is by itself.

I did all that, but he still wouldn't join me. I'm only level 6 at the moment, so I figured there was probably a minimum level requirement, but I couldn't find anything to that effect in any of the online guides I looked at.