Hate to break it to you, but spring break is considered one of the busiest seasons, right up there with Christmas and New Years' week. If there are a lot of schools out your week (and usually there are, the last two weeks in March) you can expect very high crowd levels.
We were there last year March 24th-28th (which also happened to be the week after Easter) and the parks reported record-breaking crowd levels. 90 minute waits on the big rides by afternoon and evening... and you couldn't move more than a slow shuffle through Adventureland and New Orleans Square areas.
I would just plan on following Hydroguy's tips-- be there at least 30 minutes before opening, tour with a plan in the morning, collect FPs, hop to DCA when it starts getting crowded... leave and take a midafternoon break at the hotel... come back in the evening and use your FPs you collected earlier.
Good luck!