If it's possible for you, I would seek a 2nd opinion.  I'm not a doctor, but it seems like a quick decision to start Humira.  I was on Remicade for 21/2 years after a terrible bout of what my docs decided is Crohn's.  After 21 days in the hospital, a microperforation of my pouch, and a fistula, we thought it was worth a try. One of the missing pieces were granulomas.   Everyone is different, but I would like more information from my doctor.  

I'd want to see if a course of antibiotics cleared it up first - just in case it's simply pouchitis that extended a bit beyond its usual boundaries.

Yes, that seems hasty to just start you up on Humira.  From personal experience, when I was in the hosptial last year with an obstruction, they did perform upper and lower scopes (because I was chronically getting obstructions) and came back and bluntly told me I had Crohn's and wanted to start me up on Remicade or something.  It was devastating, and I declined right away since I didn't think that was the right course of action.  Then a few days later, I get a call saying all the biopsies came back negative for Crohn's and my doctor thinks all the inflammation was from a week of obstruction and NG suction.  Then, this year, I had open surgery due to another obstruction, and they removed a ton of adhesions and said there was no evidence of Crohn's.  In a nut shell, my doctor told me this...regardless of actual diagnosis, they will treat the symptoms.  If antibiotics and such treat my pouchitis and I get along fine, we'll continue that course.  We'll entertain the ideas of the other meds once inflammation is no longer under control with our current regimen.