First I'd say go ahead and enjoy being in the condo -- true it may not have some of the Disney magic/fluff, and you may have some more travel time -- but you'll probably really be more comfortable, not crowded, and it's really helpful to have some kitchen use. And you may have a lot shorter walk back to the condo at night, than you'd have at an onsite property (unless you were on the monorail).
Pretty much go at the pace of your son and see what he might like to do -- maybe start with Buzz Lightyear, or just the train around the park. It's great that he likes characters -- be sure to use PhotoPass a lot, some with all of you, and with some of him, and maybe switch off with each of the adults a few times (get a variety of photos). The Aladdin ride can be a good starter -- you don't have to go up high right away. He'll probably enjoy the Boneyard at AK, and the train out to Conservation Station. At Epcot -- go see Turtle Talk with Crush, and Spaceship Earth (DGS loves rollercoasters, but he asks to go on SE, because it goes sloooooooooow). Lights, Motors, Action at MGM (another place where ear protectors can be good) -- it's boring for me, but boys like it.
If the shows and fireworks are too loud for him -- get a pair of ear protectors (at hardware or sporting goods store) -- they seem big, but can help a kid have a happy experience. The last couple of trips with my DGS (at age 6), I took a stroller most days -- it was helpful for hauling along helpful stuff, and then he had a place to sit in the evenings for parades and fireworks (and sometimes he was just so tuckered he needed it).
Hopefully your folks won't feel pressured to max out on "doing" everything, esp rides -- there's lots to see and do without the rides. Visit the area in the town hall on main street behind the kodak center -- fun place to take some photos and see old cartoons.
Have a wonderful time -- you will create some great memories!
