First of all,

to the disABILITIES! Forum.
Someone else may be able to give information about wish-granting organizations that will work with adults. When Judy was diagnosed with cancer we had both been retired and moved down here less than six months previously.
The first suggestion I have is to make sure that he uses either a wheelchair or, if he is able to drive it, an
ECV.
Yes, we are bringing his wheelchair. I haven't decided on the ECV yet. I'm sure it would help, but I also wonder how much it will impact getting around. We don't have an accessible vehicle of our own. Right now he only uses his wheelchair at work when he gets tired, so we don't have a lot of experience in actually moving around with one. I'll have to do more research on that.
If he has invisible needs, such as being out of the sun due to chemotherapy (check with the doctor) or vision problems and needs to sit up close at a show (since most wheelchair seating is at the back), obtain a Guest Assistance Card at the Guest Relations Office of the first park you go to. (See the "disABILITIES! FAQ" which is the first sticky at the index for more about the GAC.)
I'm sure he will need a GAC. I think I read that he doesn't need a doctor's note to get it, but we'll probably feel more comfortable having a note. He does have invisible needs.
If you will be staying on property I would suggest investing in a deluxe hotel for several reasons. One is that for some of them you do not have to go outside to get to a restaurant. Another is if there is a need you can get meals sent using room service. Also, they tend to have better park transportation available.
Unfortunately, with 6 people in the family, it just isn't an option. We are staying at POP and even that is pushing the financial limits a lot. I did opt for a preferred room location to minimize the distance to/from the food court, etc.
If he does get worn out and needs to rest, you can take him to First Aid at any park and they can give him a place to lie down for a while.
Thanks for the info. That is one of the main reasons we decided to stay on property. If he needs to go back to the room, we can separate from the kids and still have transportation. I'm sure he will be very limited on how much he can do in a day. I really appreciate your help