I agree, very doable, as long as DD doesn't sleep late. My DW is a school teacher so we always do March break (summer is for camping). It is a bit tougher now that both my kids are teens (and DS is a sleeper) but we force an early start. I have heard many people complaining about crowd levels during break here on the Canadian board, and I can only assume they are late starters. We NEVER see the kind of crowds they talk about!
The only advice I have is to read the Unoffical Guide and follow their touring plans. If you get to the parks early and have a plan, you can ride all the best rides with very short waits, and be back at the pool or shopping DTD by mid afternoon just as the crowds are peaking at the parks. Head back in the evening if you want to see the parades or shows.
Go for it, and have a great trip! You get so few years to make memories with the kids, take advantage how ever you can...