Whether you take it all the time or only as needed is a call for your doctor to make. I suspect he will want you to take it in good times or bad. You don't need steroids. Diet plays no role. Calcium has nothing to do with it.
Whirlpools help keep the back limber, and yes, swimming provides good exercise without back stress.
Some patients turn to a physiatrist to tailor a program. Not a bad idea. You sound like a great patient. I hope all goes well. I have it and have been told that exercise can be hazardous for me.