Just go, beautiful country, great people (really nice), amazing food and even still cheap.
Two English friends were riding two XT 660 R, so at least, no limit at 650.

(I think/am almost sure there is not limit, but cannot confirm it myself).
Snow should not a problem at that time. We rode with very improper gear (thin raincoat) in November with no worries, not even cold. Only in December it started to be a little colder. So, get ready to extend your visas (yes, you can get it on arrival to the border).
Roads are just great fun, and you will the quickest, be sure (at least, we were on Pulsar 150cc!

). Enjoy Siddharta highway from Lumbini to Pokhara. And do not miss a trekking, just beautiful, you can rent any gear there or buy North FAKE.
Enjoy the trip,
Esteban
PS: If coming from India, get updated info about returning in a 3 months period (they are just a pain!).