We have gone around the holidays for several years. Sometimes early Dec. sometimes late Dec/early Jan.. Twice we have had freezing weather - literally 32F or a bit lower, so pack a nice warm outfit just in case. Other years it's
much warmer & I can't remember it ever raining, altho' it must have at some pt..
Favorite things associated w/ the holidays:
Checking out the decorations in each park, they are so well done & I love the huge trees w/ their oversized decorations in front of each park.
Epcot - special illuminations, browsing the countries' stores looking at Christmas ornaments, watching the glass blower in Germany make ornaments, slipping out the International Gate between France and England to go look at the Chocolate life size carousel in the Beach Club lobby. The Boardwalk a short walk away is worth a look as well.
MK - Seeing Main Street all decked out for the holidays, the Jingle cruise which is a special Christmas version of the jungle cruise including appropriately corny holiday themed jokes, browsing shops for ornaments, taking the monorail over to the GF to gaze in awe at their tree, buying a chunk of gingerbread from their lifesize gingerbread house and munching on it while sitting in the lobby and listening to the Christmas carols being played on the grand piano by the pianist. Taking the boat out to the WL, grabbing some hot chocolate and sitting in one of the chairs in front of that huge fireplace while admiring the huge multistory tree there. Taking the boat back in time to see the water parade.
DHS - used to be Osborne lights, alas...sigh
AK - AKL has a ginormous tree worth seeing so worth a quick hop over to check it out on an AK day or if you're dinning at Boma or Jiko.
And I must visit the Christmas store at Disney Springs because you can never shop too much for ornaments

On my list of things to do: wagon ride at Fort Wilderness & seeing more of the decorated campsites (I've only seen a few.)