Hi Heather,
Wow, you really have my gears working to find you an answer for this question. As a parent of a child with Asperger's I realize how important this question is to you. Everyone wants to enjoy the fun at the Walt Disney World Resorts.
I usually tell first time guests to visit EPCOT first. However, the rides are in the dark (Ellen's Energy Adventure, Maelstrom or Soarin'). Nemo in the Living Seas pretends you are underwater but there are some scenes which you will see a shark or an interesting sea creature. Spaceship Earth takes you on a journey through history but parts are in the dark as well.
This being said I think I will send you to Magic Kingdom and try the
Jungle Cruise or the
Magic Carpets of Aladdin. Both are outdoors and you can sit with your son. They also simulate the types of cars or boats you will be travelling in for many of the attractions. You can then hit Tiki Room. If dark is not an issue, Pirates of the Caribbean is up next. There is a holographs scene of Davy Jones which opens the ride but then you have just pirates being pirates.
If you think your pirate will need shorter wait times, head to guest services and obtain a Guest Assistance Card (GAC). This will allow you to reduce your wait time on the rides. You simply show the pass to the cast member at the front of the queue and they will direct you.
If you have a question about a specific ride, please send me a follow up question.
Have an amazing vacation!
Beth