We have traveled numerous times to WDW with friends who's son is on the spectrum. Our friends son was 10 the first time we went and his 14 now. His real issues then were noise, crowds, and food. While they had an attraction pass for him, many times FP+ worked well too so he wouldn't have issues in lines for more than a few minutes. WDW dining is fantastic with food allergies or dietary requirements, just ask at any location and they'll work with you. Our friends take their son to the pool every morning to help their son burn off some energy and relaxed him for a nice afternoon in the parks. Obviously, every child is different, but navigating around crowds (where possible these days), avoiding really loud attractions, etc. really made it a great trip for him. He loves it now, but I know they've had days of challenges so flexibility and knowing the transportation system for quick escapes to the room is a real help!
Hope you all have a great trip!