Others have given you good advice. As far as keeping teenagers busy after parks close, my son was (is) a sports freak. Disney has 3 or 4 ESPN channels on their TVs, my son was perfectly content after a day in the parks parking himself in front of the TV and watching sports, I was perfectly content tuning it out and reading.
As far a weather, I've been in Dec. and in Feb. I'm from Georgia so, for me, cold is anything below 50. Most years in Dec. I've gotten by with a lighter coat and a scarf, we have actually used the pool a few times in Dec. In Feb., I was freezing. It was cold and rainy/drizzling all day on some days. I wore gloves, wool cap, knit scarf, tights under leggings, 3 layers of shirts and a heavier jacket and was cold the entire trip. We had fun and would do it again (little did we know the parks would close down in a month), but I actually prefer the late spring to fall months. I'm a hot weather gal.