Dave,
Fort Wilderness has both external and internal busses. All of the campground loops have a bus stop. You walk to the bus stop, which is a very short walk, get on an internal bus, and then go to either end of the campgroud, where you can then either take the bus (at one end of the campground) directly to the Disney Parks, or (at the other end of the campground) take the boat directly to the Magic Kingdom.
I would suggest you google up a map of Fort Wilderness to check out the campground loops. Some are close to the pool and its store, some are close to the marina and its store, some are close to the main bus area. You would have to decide which area you want to be closest to. Fort Wilderness is big.
Disney busses do allow mobility scooters. People with scooters and their families are the first to board. Bus drivers lower a ramp to get you on the bus.
I would suggest you go to www.disboards.com and look under Camping. There are very knowledgeable people who can help with the other questions you have.
Hope this helps.