My DW and I were down the week before Easter last year. The weather was fine except for the rain from a cold front that was hanging around the area. Every day was somewhat cloudy if not rainy, but we live just two hours north of Orlando and the two or three weeks before our trip had been pretty much without any rain at all. So there is no way to say for sure. The worst winter storm I can remember was from March of 1996? The No Name Hurricane that came through and left 70 mph winds, tornados, snow, etc. all over the southeastern US, including Florida. That was fun
But generally March is comfortable weather that can slide either into the cooler temps or warmer temps, is often breezy, and sometimes rains. Cant get much more detailed than that until you get about a week away from your trip. I will say that you should bring at least one warm outfit just in case, and rain gear just in case, but expect mostly warm weather. Swimming should not be a problem at all unless there is a freak cold front.