I think they should be light because it is after Easter/Spring recesses. We are also going to Orlando (Uso and Captiva) during this time and we had no problem getting reservations.
We went last year during that time 4/22-4/30 2005. You may have some Spring breakers but it should still be wonderful for you. Easter is later this year so that maybe a factor. Last year Easter was in March. We had no problems with crowds and the weather was beautiful
Realistically, it should be somewhat busy. You will have schools on Spring Break during that week. I was there last year at the same time and there were schools on Spring Break from Brooklyn and several other school systems. Grad Nights are not that much of a factor except on weekends. I would rate the crowds last April a 7 out of 10.