Hi and welcome. I don't have any experience with either biologics or methotrexate, so won't comment on those. I do a low starch diet rather than a no-starch one (loosely following Carol Sinclairs "IBS low starch diet" book). It does enough for me to not want to bother with the extra effort of no starch at the moment. Itgs all individual though - some folk do seem to have to go absolutely strictly no starch for it to work, and some don't get a positive response either way.

As far as the exercise goes, there are some good stretches to do to help retain flexibility. You should be able to find these on one of the AS society sites. NASS (the Uk one) definitely has a downloadable brochure of exercises.