Hi. Our DS is 13 and LOVED WDW. He has been watching Disney videos from the time he was little, and we've had vacation planning videos all the way back to the mid-80s, so he was very comfortable with it all. He asks every week to go back, and you know what, we are - in August. He's already excited about it.
A few things that we learned:
1. Use companion bathrooms. These are separate rooms that he could go in with my DH and not be subjected to the noise and echos of the big bathrooms. He also is not what I'd considered 100% trained, so having a separate area and patience was great.
2. First-aid stations have rooms that you can take him to if he's having a meltdown and can't get out of the park fast enough.
3. The Guest Assistance Card is invaluable. Use it.
4. I don't know how verbal your son is, mine is fairly verbal but tries to get away with 1 word answers. We used Disney to improve communication whenever we could.
5. Practice going to restaurants, malls, any large group settings that you can and remind him, "when we go to Disney World, we will have to sit in a restaurant and order our dinner, wait in line ...."
6. Relax and have fun. All of our kids are different - enjoy the world WITH him, don't think you have to force him to adhere to anyone else's idea of how he should act, look, talk or feel.
7. All of the cast members were GREAT with him. So were the characters - I think a lot of them are trained to recognize autism now.
8. If you can, go at a slow time of year. We went in January and the crowds were barely noticeable.
He's in my sig and here on the trolley: