Last year we went end of Nov - early Dec and this year we were there Jan 10 - Jan 15. Both times we have had a variety of weather. I just pack for everything. This year we had temps from 32 to 70.
I pack long sleeved tshirts, turtlenecks, short sleeved tshirts, a hoodie, a windbreaker with a hood for rain, jeans, one pair of capris, gloves and a scarf. I layer my tshirts and have the hoodie on in the morning. I can tie the hoodie around my waist if it warms up. If it gets even warmer I can always duck in the bathroom and take the long sleeved tshirt off, leaving just a short sleeved tshirt. This past year I think I only had one day that I didn't wear my hoodie all day. I never needed the capris this year either.
Jan 10th was the last day of the marathon weekend. We did see people around wearing medals when we were at Epcot but didn't think it was crowded. We didn't get to Epcot until just after 4 pm that day.