Imuran is a pretty safe drug for most people. I've been on 6MP (its sister med) for a couple of years with zero side-effects. You may get nausea for a week or two after first starting it - that's normal and goes away for the vast majority of people. As for rarer, more serious, side-effects, that's what the blood tests are there for: to detect any problems. I would strongly recommend going on Imuran, but it does take up to 3 months to start working - it's a slow-acting drug.
As for the SCD diet, it can
work but I would take the amazing testimonials with a pinch of salt. Not to discourage you but I've seen a lot of people on the Crohn's and UC forum whom it hasn't helped. But you won't know unless you try it, so by all means give it a go for a few months and see how it goes. Or consider trying the IBD-Aid diet, which is an updated version of the SCD and slightly less restrictive. /www.ncbi.nlm.nih.gov/pmc/articles/PMC3896778/
High drop off rate, but of the ones who stuck with the diet everybody saw an improvement in their symptoms although nobody appeared to go completely into remission on the diet.