We went in May a few years ago with our 3 autistic children. They are high functioning but 2 hate crowds, one especially.
Best thing we did was being there at rope drop (at Mk we stood by front wall, other places we tried to find wall, boys stood along wall, we stood between them and crowd) Then I had detailed touring plan. My kids like to know what is coming up, so we had a book about rides and they looked at pictures and knew where we were going and in what order. I even picked out where we were eating and they new that. My daughter would say, now we go___________. Very helpful for us. Checking restaurant menus ahead made sure I knew there was something they would eat. We took a pbj for my daughter a few days
Last helpful thing was leaving around 1-2 most everyday. A couple days we went back. But having the break from the crowds was as important as the break from the heat
It was worth the pre planning, if nothing else I knew what was coming up and felt more in control, so when something went wrong I had an idea where to go to get cool, out of the crowd, or a drink, etc
One son was in a wheelchair so we didn't get a GAC but honestly it was more trouble and we hated having to use it, he has had surgery now and is looking forward to going back and not needing it. He got so sad sitting there watching others load, he didn't remember the times it was faster, and he could get out and load regular, just not stand and walk long.
The plan was much much more helpful (not that I wouldn't get a GAC, just our experience)