The two Easter weeks are April 5 to April 18, with Easter the 12th. Those two weeks will be more crowded than you can ever imagine unless you have gone the Easter weeks or Christmas week before (easy way to look at it, Soarin' will have a 3 1/2 to 4 hour stand-by line almost all day except early morning).
Week beginning March 29 and ending April 4 will be very crowded but only about 1/2 the crowd of those two Easter weeks. Nevertheless, you will still see many long stand-by lines (Soarin to 2 to even 3 hours some times of day and other populars going to 90 minutes and possibly longer many times of day). If you do not already have dinner reservations, you better try to make them immediately (and you might not get many things you want even now).