Hi Lauren! Spring break season is indeed a busy time at Walt Disney World. But with careful planning you can accomplish a lot and still have a magical time.
Your plan is aggressive as far as trying to get it done but that is because transportation can be more of an issue during the busy times of year. There are more cars on the roads and there is quite a bit of construction going on right now making traffic even more of a challenge.
The great
Hoop Dee Doo Musical Revue is a favorite dinner show for my family. We love the food and the entertainment and never get tired of the wonderful jokes and great singing. Since you have reservations for the 4pm show you will want to leave the Magic Kingdom no later then 2:30. The boat to Fort Wilderness can be found directly in front of the entrance making this very convenient. Check in should be done for the show at least 30 minutes ahead. While you wait you can visit the Disney stables or have the kids play on the playground or with the games set aside on the porch.
Your biggest challenge will be once the show is over. You will want to hop on an internal bus just outside Pioneer Hall that will take you up to the front of the resort. There you will need to transfer to the Hollywood Studios bus. Obviously there is no way to know if your timing will be good or bad as far as waiting on the park bus. Depending on what time Fantasmic is that night will determine if this is possible. You might not arrive to the Studios until 6:30/7 and you should always plan for delays.
We often try to make some tight reservations and plans but I don't suggest you do this for your entire trip or you will be exhausted by the end of vacation and need another. I completely understand though as there are so many wonderful things to see and do at Walt Disney World and for most of us we want to do it all.