Can I make a suggestion? My kiddo is also autistic with SPD. For a few trips, it was really difficult to manage. He struggled mostly with long lines. THATS where fast passes are helpful. Bringing a SPD child and expecting them to stand in line for an hour is a lot. The whole thing is a LOT.
So the fast passes helped, but you only get 3. so.... theres that. But we found out about
DAS and it has made a HUGE difference. A cast member suggested it after my then 4 year old tried to climb over the wall at Small World And then screamed and kicked like a psycho while I tried to hold him for the rest of the wait. Smiling and saying "sorry...he struggles in line" was embatrassing for me- but the experience was miserable for him AND for those around him.
A DAS is an access pass while you wait in a virtual line instead of in person. You can get it at the front of the park and its good for your length of stay. You tell them that your child has additional sensory needs and standing in line may be overhwhelming.
Of course this isnt right for every family, but when you have a child who would not be able to go on rides with long lines bevause of their disability, its a lifesaver.
As far as magic kingdom goes? Anything but space mnt, splash mnt, 7 dwarves and big thunder my infant nephew goes on. Hes 1.
Additionally, haunted mansion is a little ghost-y and pirates of the carribean has some shooting of cannons that maybe loud and a SLIGHT drop (there arent even buckles-its that slight). But both are family friendly. Everything else is whole-family.
For hollywood studios.... torror of terror and rockin rollercoaster are probably out. Star wars is fun and my 6 year old loved it-but it can feel fast, which can be a little intense. Not scary- just intense. Its a 3d ride.
Toy story mania is family friendly. Slinky dog is a small roller coaster. Alien saucers has height resctrictions because hiofow it spins-but not scary and totally appropriate for a 6 year old.
I think thats actually it?
HS is more about the shows. The frozen sing a long is a MUST DO. Do NOT miss it. Its the best thing in the park. they also have a disney jr one, indiana jones (loud!), beauty and the beast and little mermaid.
Dont think I missed any! Good luck!