I enjoyed a brief stay at WDW this past March (see below), and found the weather to be fine. Warm to hot in the afternoons, and pleasant in the evenings.
I visited in March especially to watch a couple of Atlanta Braves spring training games (hot sitting in the sun during afternoon games), but also visited three of the parks while I was there.
The parks were generally quite crowded, (especially Epcot during an evening extra hours day), but with advance planning I had no problem doing the things I wanted to do. Be sure to made advance meal reservations.
Enjoy.