I think crowd wise, you'll be fine! Not a lot of schools get off that early! It'll probably start picking up towards the end of your trip, but not a lot (expect people to start really coming in that first weekend...but you wont be there so there shouldn't be much to worry about!)
Weather might be chilly! Its always wise to pack for both chilly and warm weather! (Technically its still winter that early in march!) I agree with pp 70's during the day, 50's at night! This past january it was in the 80's and that was unusual! So you just never know with Florida weather!
Have a great trip!