I go in March.
2 years ago we went 3/10-3/17, That year Easter was in April. We had a great time, cool in the am, hot all day, cool in pm. Crowds were manageable. We did everything we wanted to. Had tons of fun. Only the Saturday was really bad at MK. But the park hours were just extended, so we had lots of time.
This past March we went 3/20-3/30, Through Easter. We had a good time, hot, hot, hot. Crowds were intense, PS were needed everywhere for every meal. We did everything we wanted to do. Had tons of fun, but would never do 10 days, or a trip at Spring Break if possible. Yes we were at MK at 2:30am with 7yo's at MK riding Splash Mountain.
Next year we are going either 3/4-3/11 or 3/11-3/18. We are leaning toward 3/11-18 due to DH's work. But I think you will be fine in the first 2 weeks, after that you will be starting to hit college spring breaks. The park hours will be extended, but just don't think you will have the park to yourself. Read about Fast PAss, and make sure you make PS. Make a list of must do's, you will have a great time. It does rain 1-2 days.