This great post might answer some of your questions if not all. https://www.reddit.com/r/AskHistorians/comments/1y6slo/when_the_mongols_were_poised_to_attack_europe_how/

I’m not a historian, just a guy interested in history but /u/rakony seems to be very thorough and well researched in anything regarding the Mongols. I hope it helps!