Weather will be "changeable". It could be warm one day and chilly the next. A friend of mine goes down regularly in mid-February and admitted recently that they've never had it warm enough at that time to really enjoy the water parks. Warm enough to swim but not stay out in the air for slides, etc.
Crowds prior to Presidents Day should be normal and bump up as you get further into February. Remember February-March is prime tourist time for all of Florida, not just WDW. The crowds should be manageable but it won't be empty.