I agree that the WDW strollers are great. My 8 year old son still uses the strollers-it's enclosed on three sides, so he can hide himself and cut down the excess visual stimuli.
A baseball cap also helps in cutting down the visual, as does a towel. My son normally doesn't want anything on his head, but at WDW, he'll wear his cap. In fact, a few months back, he left his hat in the stroller at MK. We were leaving and they were doing Night of Joy. He was absolutely distraught. A CM at the gate saw the situation-and was wonderful. She escorted my son and me back in to try to locate the cap-no luck. We were given a 'no strings attached' to get him another one. He was still extremely upset, as he felt that his cap was the only one to help him.
Fortunately, it turned up the next day and we got it. Any parent with a child on the spectrum can imagine what we endured for those 15 hours!
I dress my boys in Orange shirts-it started because I only seemed to find
Disney store Buzz Lightyear shirts that color, but then it became a routine to buy any orange shirts. It really makes it easier to find your child in the crowd.
If your child has food preferences, packing as many of the non perishables as you can to bring with you will also help. You don't have to worry about finding this things on vacation and it creates more room for the souveniers. We went through a yogurt phase-had to have yogurt (and a particular brand) at least twice a day. As a solution to that and renting a fridge, we bought a refrigerated travel cooler.
Plan for lots of breaks. Over time, we found that after 2 or 3 days, a non park morning decompressing at the pool bought us a lot more fun time later on.
There are several internet sites that stream WDW music (IIRC, live365 is one of them). Getting him familiar with the music he'll hear may also create comfort.
In the many trips (10+) before moving to Florida, and the frequent trips since moving, I've found many CM's to be very helpful.
Good luck-I'm sure you'll have great times while at the parks!
Suzanne