It is a weird dynamic, at least we are not alone. I think almost everyone that receives a trip like this is in the same boat, torn between a need for information and to plan and extreme gratitude!
Our trip is coming up, we arrive in Orlando 5/30 and stay until 6/5. They gave us a three day pass to Disney, we are doing MK on Monday (only day available, I had to ask them to give me the tickets a few weeks ago so we could reserve parks), AK on Tuesday, Relax at the resort day on Wednesday with a reservation at the Boathouse at Disney Springs for dinner, Epcot on Thursday, and we are driving to Clearwater Beach on Friday for the day. Dream Factory offered us additional passes to Universal, SeaWorld, Kennedy Space Center, but my kids thought a relaxation day to chill and do homework made sense (who are these kids?) and we love the ocean so a beach day was a definite for us (they are renting us a car for the week). I elected for Clearwater, even though it's an hour further than Cocoa Beach, my kids have never seen white sand and blue water like the Gulf of Mexico.
Getting the tickets transferred online so I could make park reservations was not smooth. Unfortunately, Hollywood Studios was already booked up by the time we were able to reserve parks, but we are just as excited about AK. I had to purchase magic bands to put our reservations on as we believed that to be necessary? I'm honestly not sure if I could have just used the My Disney Experience App or not, but $60 seemed fair for 3 days at Disney.
They gave me the flight info on Friday, which put my mind more at ease. I had a lot of questions regarding the flight itself (layovers, times) and if we were able to check bags or if that was extra. In the email my contact told me to ask her anything, we are meeting up in a week or two to do paperwork before the trip, if they don't address expenses, that is my last question. I feel so rude asking them if they are giving us money for meals etc., but I need to budget for it if not.
My advice (as I live through this situation myself and try to take it also) is to be transparent with your son. Tell him you don't have control over every aspect of the vacation, so some things may not be as you expect, but that can also be exciting and cool, as they might be even better! Part of the fun is to let the magic happen and to enjoy time with your family. I'm trying very hard to have this be a stress free trip filled with gratitude.
You could try talking to your contact about staying on site at Disney. My limited experience with Dream Factory leads me to believe that they tend to work with donations as much as possible. It sounds like the timeshare we are staying in gets utilized frequently in Orlando if GKTW is not an option. Even though it's not on site, the resort seems pretty decent, lots of pools and splash pads.
As far as your dates, my understanding is that November is a bit busier at Disney, but many of the new attractions will be open and running then. We will hopefully be that much further away from COVID, with more people vaccinated and less restrictions. July is also incredibly hot. I have done quite a bit of Disney research, and if I were given the option to choose, personally, I'd pick November.
I will come back to this thread and let you know the outcome of our trip. Keep us updated on yours also, I hope your son has an amazing time and gets to feel just like a kid for a little while with some of the stress of chronic illness suspended for a short time.