Relationships are always difficult when you want time to yourself, even if its not alot!
I don't think it would be any different than having any other relationship. Just communicate when you want your "me time" or when you are ready to do something. Any cons of the situation can be worked out through talking I would think.
Pros? uh, you don't need to put up very much effort to see eachother? I suppose to me thats a far greater pro being that I'm 3 and a half hours away from my boyfriend. So maybe I'm just not thinking straight.
Unless this girl is crazy and you think she'll be climbing your tree to enter your window at random points in the day I really wouldn't think living too close is an issue.