This is an ongoing question isn't it? I sure don't know the answer but, for what it's worth, here's a bit from my experience. When I first had the j pouch created, I was put on a clear liquid diet as many are I'm sure. Jello, fruit juice and broth. I developed pouchitis with the first few weeks. A course of antibiotics cleared it and I started on VSL#3 as recommended by the surgeon. I didn't develop pouchitis.
I later had a diverting ileostomy and then was reattached after a year or so. I thought since I was starting out with a pretty empty pouch I would do it differently. I didn't have the juice or jello as I didn't want the first thing in there to be sugar. I had broth but also plain yogurt and thin oatmeal (Pablum) after a while. I also started a probiotic right away (not VSL#3). That was about a year and a half ago. No pouchitis. Just another anecdote I realize.
Thank you for sharing your experience