In Illinois, we have Lincoln's Bday off instead of Presidents' Day. I noticed that next year, those days are a week apart! I've been trying to price a WDW vacation but it seems it's too early still.
Anyway, I saw that WDW charges more for their rooms on President's Day weekend than they do for Spring Break weeks. I think they call Pres Day weekend "peak". So, that should tell you that it is probably very busy in Orlando that weekend.
Maybe you should stick with midMarch.