Hi there, we went on our MAW trip to WDW in May of this year. We had an incredible time. I envy you the time of year you are going as it was blazing hot and humid when we went. AND you get the Christmas decorations which I'm sure are going to be fantastic.
Purple Princess - we didn't get our welcome package from our wish granter until about a week or so before our trip. It's hard to be patient isn't it?
I'm not sure how things vary from chapter to chapter, but we didn't have to really worry about much. MAW and GKTW took care of us, just about from the minute you leave until you come home, but it doesn't hurt to do the research and be prepared. A rep from GKTW met us at the airport with a luggage cart, took us to the luggage area then escorted us to the car rental place and made sure we understood the map to get to the GKTW property!
On our flight to Florida, another Wish family was on board, all the kids were invited to see the cockpit before take off and they were acknowledged by the pilot over the PA (but I'm sure that varies from pilot to pilot, as our return flight was not that way)
We did not stay at GKTW as they were fully booked but we were invited to spend as much time there as possible and eat as many meals as we could there. We were placed at a Disney hotel which was awesome, but of course a little bit of a drive from GKTW (their directions that they provide you are pretty darned good). GKTW is an incredible place. I do wish that we could have stayed there as there was so much to do. We did manage to squeeze in a bit of mini golf, splashing at the water park, fishing, horse ride, carriage ride, train ride, arcade games, a visit with Santa, a birthday party complete with a beauty queen, and of course ice cream. And keep in mind, this is all when we weren't at the parks!
The people at WDW really treat you well. Make sure that badge is very visable as that is your "ticket" to the FOTL. It makes such a huge difference, especially if your Wish child doesn't have the energy to wait in line for hours and hours. We actually didn't even ride all that many rides as our dd was mostly interested in autographs and pictures with Characters. If that is your aim, be sure to visit the Character Connections at Epcot as the classic Disney characters will pose for a group photo with your family (otherwise you line up for each character). I had read about it from another wish trip and I was in tears it was so touching. It was very special.
We had a nice time at Sea World, but the park is a bit confusing and quite large. We did not get the free photo's that I read about, so be aware that it may just depend on the knowledge of who you ask. (we ended up buying photos) The killer whale show is quite amazing. Also be aware that if you would like to feed the dolphins that the feeding times are scheduled. We went when we were ready and missed the feeding time. Oops.
I did get sick on my trip, so I will say, get lots of rest before you go, don't stress out too much and wash wash wash your hands. (I spent a full day at the hotel in the room)
The weather was a bit too hot for my kids, but they still had a fantastic time. We did as much as dd could handle then retreated to the hotel or the air conditioned car for a break, then headed back for more. You are so lucky to be going in December. I've read elsewhere that you will likely need sweatshirts or jackets for night time.
If food is very important to you, then do try to make some advanced reservations (our trip included a budget for some meals). We ate many fast food counter meals which were good, but got a bit tired after a while. Our best and only "proper" meal was at an Irish pub at Downtown Disney which was fantastic. The rotisserie chicken options at counter service was usually a nice change from hamburgers and hotdogs, and if you aren't into the huge portions, the kids meal (which includes a drink) was a good amount and a good price. I thought the food at GKTW was okay. It changed everyday and you were informed of the choices via the Village Voice newsletter everyday which was really neat. I saw the golf carts which were cool, they brought cold breakfast (and coffee) to your villa in the morning and coffee, milk cookies etc at bedtime. Pizza is always an option at dinner time if what is being offered isn't to your liking (and McDonalds is not that far away)
If you plan to see the firework shows at any of the theme parks, it is worth it to ask a CM if there is an area for wheelchairs as they are usually roped off and not crowded (if you have the pass for wheelchairs) it makes a difference when you are trying to make the most of the time and energy your child may have. Not having to wait an hour or more to get a good spot for the fireworks is a nice thing. Not all the parks may have these areas though and some parks have more than one, so ask which one is the best one, and ask early so you have time to get to it. (we asked late and then had to run)
My I have gone on haven't I? Well that's about it I think. If you have any other questions just ask. Hope you have a great time.