My favourite time at WDW!
Expect the weather to be variable--it can be in the 80s or the 30s. If you live in a cold climate, you're already set for the cold, just bring layers for everything from warm through in between. Definitely bring swimsuits. May or may not be warm enough to use them, but probably will be at least some days.
Crowds are bigger than they were a few years ago, but very manageable. You'll still need ADRs for the most popular TS restaurants and times, as well as FastPasses for the most popular rides. Never have managed a FastPass for Soarin'--I don't do mornings! And the standby line tends to be very long!