I know the weather hasn't exactly been "normal" this year but I have to ask: What sort of crowds and weather do you see in early to mid March (9th-16th)?
Spring Break will be starting for some schools during the last days of our honeymoon so there should be an increase in traffic. The Expo will be going on (as usual) so there should be about as many people as for the Food and Wine in the fall I would assume.
As for weather, I am pre-planning like I did for my only other trip to Florida (Oct 2006): rink jacket for warmth, small umbrella for the occasional shower, t-shirts and shorts, and swimming/volleyball/tennis gear just in case. I will be keeping a close eye on things as we get closer, but do you think I would need actual long pants? Is it going to be under 45 and windy in the evening or morning (the only reason for long pants)?