Welcome, Echo! 95% of the winter-spring hikers take the MR over the MMWT (Main Trail), mostly due to the distance difference. It's a lot easier to break trail in snow over 5 miles instead of 11.
There can be avalanches on both trails. I recall a report from one guy who camped in the low area just s of Iceberg Lake, and they were buried under a light avalanche, and dug themselves out! (It was stormy during their overnight.) It can happen on the MMWT too. Worst danger is right after a significant snowfall.
The MR is Class 3 in the steepest places. As for boots, I suspect the guiding companies have a supply of the plastics on hand for their clients.
