May I ask what kind of dog he is (like what service he provides)?
I don't mean to scare you with the whole waiting on a CM for a potty break. We didn't have to wait every time, but there were a couple times we had to wait for the CM we approached to get another CM who could actually take us back there.
I'm a little surprised that you're taking a dog that new... especially when you say you've never owned a dog. I guess if you had the tripped plan THEN found out you were able to get the dog...or its just the only time you can get down there, it makes more sense. My concern is it takes time to bond with any animal, and to learn its "quirks" to so speak (ie how long before they give a signal they need to potty to when they'll just go, how they react to heat/cold) and then with it being a service dog, learning how to reacts to different situations. Guide dogs from the school we went through are put through training to learn to deal with loud noises. They're put in a down/sit while guns are shot off, fireworks are set off, plates smashed and all that (from a safe distance of course) as a way to get them used to those situations so they don't flip out if it were to happen while they were at work. That being said, when we watched the JAMMinators, one of the performers started walking towards us while drumming and our dog was not happy. He stood up from his sit and barked in a "stay away" voice. Disney is consitant stimulation for a human, let alone a dog, so I urge you to be patient and prepared as your dog may not react in a way you expect.
Plan on lots of breaks, being observant of it your dog is trying to tell you something (too hot, too tired, Mom I need to poop!) and just be smart about things. Dogs don't sweat, and can overheat very quickly. The pavement gets very hot and even if he's wearing booties, it will reflect a lot of heat and the dog is a lot closer to the ground than you are. Neither of our dogs would ever tolerate something on their feet so booties were never an option, we would splash water on their paws or pour a little on the ground and let them walk through it (even at the spash and play kiddie areas) Remember he can get sunburned too, particularly on the top of his nose, so beware of that. You may be tempted to give him lots of water, but try not to. Try to do it a little at a time so he doesn't get sick. Imagine it like you suck down a whole bottle of water then take a long walk in the heat, it wouldn't feel very good and he'll feel the same way. Also resist the urge to feed him lots of ice. The cold ice can be jarring to the system, so if you do give him any, make it one or two cubes and then wait awhile.
I don't mean to make you worry or second guess yourself, I just want you to be prepared. You're taking a full conscious living critter into a very different, loud, majorly overstimulating situation and there's a lot of things to remember and be aware of. Lots of people take service animals and have great luck with it, but there's potential for things to go wrong and you have to be smart about things. You wouldn't expect a 5 year old to go all day in the heat and deal with all the stimulation and people and noise and not get tired, therefore you can't expect a dog to do it either. If you're tired or hot or thirsty, your dog probably felt that way 30 minutes before you did. Everyone preaches patience at Disney, and I think this applies even more in situations like this.