Imuran necessary before Humira - and/or during?

I've been talking with my nurse practitioner. She really wants me to be on Humira, although my symptoms are currently not too bad. Everything else I've tried (entocort, pred, asacol)-I had reactions to them. She wants to start me on Imuran for probably six months, then move to Humira. I know I've read different things on here. Is it true that I should be on the Imuran first to suppress my immune system and have less likelihood of my body developing a resistance to the Humira? Do I need to stay on the Imuran all the while I'm on the Humira? She made it sound like I should only be on Imuran for no longer than six months. I know I've seen people on here that are on Imuran forever and a day and also people on Humira with no Imuran. She also said insurance likely won't approve Humira unless the Imuran is tried first.