Hi James,
I am glad to read that your stomach troubles have eased off a little bit and that you were able to get in to see your gastro doctor sooner, rather than having to wait until next week.
It's a relief to me that this doctor was happy to see you and now seems very willing to provide you with the specialist care that you deserve. I hope the scopes provide some insight that will help you and your doc figure out the best approach on how to heal your stomach and treat the UC.
Remicade is usually prescribed for AS at a dose of 5 mg (per kg of body weight) but I take a lower dose of only 3 mg per kg and this has worked very well for me. I like the fact there is less risk exposure with a lower dose too, and I'm comfortable knowing that I can always increase my dose if I need to.
It has a demonstrated ability to treat both AS and UC that may benefit you and not be as apt to bother your stomach as mtx might. Both meds are immuno-suppressants but remi quiets one part of the immune system (TNFa), not the whole immune system like mtx does... as far as I understand. I do not know if it's contraindicated with your heart meds or rhythm troubles but these are very good questions to run past your doctors.
Whatever you learn and decide James, I truly hope you'll soon be on a path that you are personally comfortable with and that will help to improve your health and well-being.

Best wishes for getting past these tests!
mig