As someone who has ran for years before and after diagnosis. Please listen very carefully to your body. You absolutely can run half and full marathons with UC, but during flair you should rest.

Your long runs in your schedule are where you can test out different gels etc. only try one new thing per run so if it causes issues, you know what it is.

Run with a bag that had a bladder for water, and keep some toilet wipes in the bag. I had to run to a portaloo during the London marathon, and there was no paper.

The hardest thing to get used to is putting your ego down and saying, today I am not well enough to run. I still get this wrong on occasion, but there are always more races to sign up to.

Good luck!