I also have a high functioning, "but she doesn't LOOK autistic" kiddo. (I HATE that people think autism always looks one way.) Our plan for our first WDW trip is based on DL experience and advice from the DIS and other parents of spectrum kids.
We had a GAC our last trip at DL. Actually we had two- one for DD and one for me for coping with acute anxiety. I found that she really didn't need hers. Either the moments she might have needed it were covered by mine or it simply wasn't the tool that worked for us. That being the case, we're going with a
DAS for me and not for her.
We ARE getting a stroller as wheelchair tag. We don't generally hold with strollers for school aged kids but what she really needs is a place to retreat from sensory overload and it's worth the $130 to rent her a safe haven. We'll be handling the airports without one, but I think she can cope with that. We've already started talking about TSA and how that will go down.
We're taking her ear coverings. The difference between a happy moment and a meltdown is often the presence or absence of her ear protection. Best $20 we ever spent.
There has been a lot of pre-planning and watching you tube videos. We've looked at maps and talked about menus and we're doing very little seat-of-the-pants this first trip. We're not planning ride order or specifics to that extreme but we're on the DxDDP and our break times are planned as meals and we'll be able to give her a basic order of the day between that and FP+.
We find that the grown ups having a plan but not telling her all the details works best. If you say "we're riding Small World and then Peter Pan" you cannot then go ride PP first because the line is short. We're better off with, "we'll be doing a couple rides" or "we're doing Small World and Peter Pan but we don't know which one will be first."
We're also going for long enough that if we need to ditch part of a day or even a whole day, we'll do it. We have 10 days and 2 non-park days and while it would not be ideal we can afford to lose our ADRs and our FP+ in order to shift things to keep her steady. We have the advantage of our other kid being older. He turns 18 just before our trip and he'll either be understanding of her needs or go do stuff on his own. He'd be perfectly content with a day at DHS, keeping the ADRs for himself and riding Star Tours over and over. With multiple little ones I'd say be prepared to split the party. Sometimes one parent needs to suck it up and deal with the special needs while the other makes sure the other kids aren't getting shorted.