from our experience, we love going in jan. my boyfriend and i have been going for the last 2 years in jan and we'll be there the same time as you this year again. last year the weather was mild, i wore capris and t-shirts most of the time. coming from mass, it's much warmer down in fla in jan. there was one day where it poured buckets for almost half the day, the rest of the days were clear. as edna said, it can get cold at night. i usually changed half way through the day to put jeans on at night, especially if we were spending time in the parks. two years ago, we went during mlk weekend and it was HOT! i couldn't believe it. i had brought capris and jeans to wear, thinking that it was going to be mild and i never wore the jeans, not even at night. i only used a lightweight long sleeve shirt. i would bring both jeans and shorts/capris and definitely a long sleeved shirt for night. i'm also bringing a lightweight packable rain coat this year (and maybe a tiny umbrella), since we did not expect that rain last year and were stuck in the animal kingdom bus stop area for over an hour.
the crowds are manageable, but marathon weekend you'll see a lot more people checking in at POP. last year we were there marathon weekend and POP was packed. the crowds in the park weren't terrible, definitely not summer crowds, which is a good thing!
