Yes it is good because you can find snow but there are a lot of chances with land slides in that season. I experienced it once when I visited sikkhim in the month of December so take precautions before you go.
Offcourse...as it's winter in dec...u may experience amazing snow....if u r snow person u will enjoy a lot...but sometimes roads may b closed due to heavy snowfalls...which may turn up into major issues as ur upcoming days and bookings for various places in Sikkim may b wasted...for travelling to various places like yumthang, gurudongmar lake, nathula pass u need permit...and u may not get the permit as these places are on heights, rather they are on peak...so do check the weather before booking anything in sikkim
Yes. I would say its the best time to visit those places. Though it would be cold, definitely you can enjoy. Plan your trip during the Tea and Tourism festival of Darjeeling which will be held sometime in December.
Absolutely Yes, by the mid Dec even the peak season comes to an end so it is easy to find a reasonable hotel or homestay. And the weather also remains perfect during Dec.But still do carry few warm layers of cloths so that u can put them on during morning and at evening time.