I would get some head phones for him, you may not think loud noises bother him , but when you put them together with the visual noise, new smells, crowds. And new environment, noise level will play a part. And some of those indoor rides are loud! Watch YouTube videos on rides to show him what the are like, and look at videos of what it will be like walking around Disney. If he can see that there will be crowds it may help him work that out. I know you said it will be just you and him, but while inline, use yourself as a buffer , between you and other people, have a safe word that he can use. So when he feels that he is becoming overwhelmed, he can say his safe word and you can leave, without the pressure of him try to convince you he needs to leave. Have some visual cue card schedule made up, so he will know what you are doing that day, so it can be printed or hand written before you leave your room for the day, make a social story about your trips and the behavior you expect, I like using the website... The Waston institute , they allow you to download their social stories and then you can edit them inserting your own ideas, pictures and names etc,it's a free site. take a couple of small things for him to use/ play with while in line. Hope you both have A great time.