Ok phew!!! Long sessions are pretty tough to handle, I was wondering how much you'd be doing at once and 3 hour sessions are perfect, I don't think it's wussy at all!!! I did the mistake of doing 6 hour sessions for my tribal and it was murder. My arm was swollen to my wrist, I looked like I had a Popeye arm it was so big and it hurt for a week non-stop. None of my other tats hurt nearly as much as that.
Good luck on getting your tat done, it sounds like it'll be AMAZING!