We've been March Break a couple of times. It is not too crazy, although, you have to get to the parks early and use fastpass as much as possible. (have a fast pass runner, and get a second one before using the first)
My kids don't like waiting for characters, so we usually don't. I just make sure I book a couple of character meals so they get their fix that way.
My boys always manage to swim. Being from Northern Ontario they will swim as soon as it gets above 15 degrees C and the sun is shining.
I have taken SW out of Buffalo. You just have to book as soon as the flights come out. I waited a day or 2 to decide on my exact dates and ended up paying at least $50 more per ticket.
We are going to St. Petes and Universal for the week before the break and the week of the break in 2009. I can get Delta flights for $761 for 4 of us right now. I'm not sure if I trust Delta not to make too many changes to the flight, or if I should just wait for SW.