Didn't know there was a cars land. Of course I will give you any advice I can. Anything specific? Like I say, there were only 2 - well actually 3 attractions I had to transfer onto- I recommend skipping spaceship earth. The rest - and I can't remember all the attractions we rode- were all wheelchair accessible. ( Wheelchair goes on the ride vehicle.)
And the shows are fantastic- all wheelchair accessible. If your son is very physically disabled, he might find the shows the most fun- although as I say most rides are now handicapped accessible, and if a person can transfer him onto one or two things.
And the characters- oh the characters. You will make me cry. No worries there. I don't care how physically or mentally handicapped your son is. Doesn't matter if he's non verbal- he will have a GREAT time! I recommend FastPasses, although generally speaking the Cast Members will put you in a special line , and either have your party or a group of handicapped parties meet characters in a special area set aside for this. Highly recommend Storybook Circus- Magic Kingdom- Talking Mickey- Magic Kingdom- and Adventurous Outpost - Animal Kingdom. Best - most accessible meet and greets. Magic Kingdom always has characters out and about too. Best place to see them. To see Mickey and Minnie enfold brain damaged children in their arms, take them on their laps- never seen anything like it. So no worries there. I know your son would love Hollywood Studios, but to be be honest, not very handicapped friendly. Neither is Epcot. It's Disney, and heaven knows they are, but just saying, better to focus on Magic Kingdom and Animal Kingdom. Don't know what resort you guys are staying in, but Animal Kingdom has transport to and from all hotels via handicapped accessible bus. And if you're staying at Contemporary , Polynesia Village, or Grand Floridian - I HIGHLY recommend- pricey, but most accessible, and comfortable- then you'll be on the monorail- handicapped accessible- and a short ride to both Magic Kingdom and Epcot- although focus on Animal Kingdom and Magic Kingdom- as they would be the most accessible and enjoyable to your son- especially if your visit is a relatively short one. I must warn you if your resort is not on the monorail- then more time is going to be spent worrying about transportation for your son, and he's going to have less time to enjoy the parks. Really worth the extra money. And don't worry about focusing on 2 parks and skipping the other 2- because you aren't missing out, and the most important thing is that your son enjoys himself to the max right? Have a magical time, and if I can answer any more questions write me another message , and I will! And please post photos of your trip!