Honestly, I'd just do three days at one place.
I live on the Atlantic and you're looking at an hour to an hour and a half drive. While you're out here you can goto Kennedy Space Center. They have a new Shuttle Launch Simulator that is SIMILAR to Mission Space in Epcot. The one thing they simulate with the Shuttle Launch Simulator that isn't in Mission Space is weightlessness. Beach days are hit-or-miss, unless you have a wetsuit. The beaches are okay, but plating in the surf around here can hurt. There's a hard shelf of rock that can cut your feet, or your knees when you fall.
Tampa is going to be a two to three hour drive from Disney. Along the way you can stop at Busch Gardens. They have a ton of roller coasters. When you're in Tampa I'd also goto the Florida Aquarium. They had a lot of stuff for kids and it's one of the better aquariums I've been to. The beach there is probably going to be easier to play in as well.
So if you don't mind the drive, I'd take two days in Tampa and one in Coco/Cape Canaveral.