Well we went last year and it was cold! We're going again this year and I will start watching the weather early in the week, then pack accordingly. On my shopping list is lightweight thermal undershirts(DH has 2sets and thinks they are great), convertable pants(DH and the boys already have them) and hats and gloves. Hopefully I will not need these, but will purchase to cover my bases.
We're staying at SSR in a 2br so I have the advantage of a washer and dryer in the room, so if I pack a combo of things I can do a couple of loads if the weather deviates from forcast(which it probably will).
We're going down Sunday before this year(did Saturday last yr). The crowds were not bad until Wednesday,really noticed that morning at the bus stop. We did MK and Epcot early in the week. MGM on Wednesday and AK on Thanksgiving. This time we'll cut the park visits off at Wednesday early afternoon.