Hi Rebecca!
I love hearing from other parents who are looking to take their toddlers/preschoolers to Walt Disney World. I took my daughter for her first visit when she was 7-months old, and my son made his first visit when he was only 4-months old. That being said, I have a few tips that I hope will help:
Tip #1: Since you'll be staying at Disney's Fort Wilderness Resort, transportation to and from the theme parks should be easy. Therefore, I would plan to come back for a mid-day nap so your son can recharge his batteries. It'll make your time together in the afternoons/evenings a lot easier!
Tip #2: If you choose to experience the shows, parades, or fireworks displays, try to scope out a spot that lends itself well to a quick getaway in the event your son changes his mind and decides he wants a change of scenery.
Tip #3: Keep your schedule rather loose and try not to rush between planned stops. Some of the most precious memories I have with my children at Walt Disney World came from spontaneous experiences that we stumbled upon in our travels.
As far as the attractions go, all four theme parks offer amazing sensory experiences for toddlers/preschoolers. The only attractions I avoid with my children are the ones with height restrictions or cautions for special effects being used. Believe it or not, there are a lot of attractions and shows that don't have any special restrictions. We've hit most of them and have never had a problem.
My advice would be to talk to your son and give him an understanding of what he can expect in an attraction or show before you hop in line. From there, you can follow the sage advice my driving instructor gave me when I was 15: "If in doubt....don't."
I hope that helps! If you should have any further questions, or want my opinion on specific attractions, please feel free to write back and I'll be happy to help in any way that I can.
Best regards,
Derek