I do not have any experiences with strictures of the J-pouch, but I would highly recommend talking to your gastro about those important questions.
When you are talking about leakage, are you talking about leakage in the J-pouch sites like the anastomosis site or leakage out of the anus??? If you are talking about leakage out of the anus then that this not something I would be as worried about as having strictures. Strictures can be pretty serious, leakage out of the anus can be worrisome but not as bad as strictures are.
I would go ahead and get the dialations done with doctor/surgeon and if there is more leakage out of the anus, I am sure they are things that can help it, diapers for example. I wore diapers my early days of takedown and they are pretty helpful. I am sure everything will be fine.