hey Ros, I would love to join u in Mongolia if I had viewed this forum earlier! Have a nice trip and do let me know how ur trip went. I would love to view ur presentation when u are ready.
best time to trek in Nepal is from Oct to Nov. It is not so cold and less snow so easier to trek. I went in Dec. The amount of snow is horrendous and consequently the avalanche risk. But in Himalayas, you can never be sure about weather as you already know. Just be careful, when it snows for say 2 to 3 days, try not to cross the pass immediately. Let the snow consolidate or melt first then attempt the crossing. Make sure you start early in the morning before the sun melts the snow/ice. once you cross the pass, it is a steep steep drop down (and icy too). A good walking stick will save your knees!
Enjoy the hotsprings in Tatopani!