I've never found medical marijuana to be much of a magical drug for my treatment, I would highly avoid attempting to replace any doctor prescribed drug with cannabis. Unless the prescribed drug is causing serious issues I wouldn't stop taking it; and if you do make sure your doctor is aware.
Keep in mind that doctors have to rely on scientific data, and for a multitude of reasons that is incredibly difficult with marijuana. Even if we did have numerous trials with various cannabis strains specific for crohns, doctors need to know what dosing you are on - which is almost impossible with cannabis. It's getting better, but even many highly reviewed edibles with their dosage levels included have been shown in independent tests to often be wildly inaccurate. That commercial grade brownie today may not be the same strength level as the one you get next week; this has been my biggest source of frustration with using cannabis as medicine.
With that said I'm not saying don't try MMJ - if it helps you then it's absolutely worth it, but in my experience I've found whenever I stop taking my doctor's prescribed meds I start to fall back towards a flare. I would say at least it should be considered to be used in addition to your other meds, but not in replacement of. I would at least wait until your symptoms improve before backing off of some of the prescription medications, and as always do this with your doctor aware of your intentions.
Is there a particular reason you don't want to start 6MP? I've been on it numerous times and it usually helps for short term use, and doesn't come with any noticeable side effects that I've experienced. Prednisone is a different story, it usually brings me out of a flare but also comes with a bunch of side effects making it not a very fun drug to go on.