I can't tell for sure, but is this your first trip to WDW? If you can give us some more details about your travel plans, mode, etc and we can give more detailed answers as to what you can expect and plan for.
We MAY be the "older couple" with the handicap children referred to above. If so, I'm not sure we're experts, but we have been there for a dozen or so years at least once a year with strollers and/or wheelchairs. We foster and adopt special needs kids, the three of which we now have are DD12, DD13, and DS13. We tow a cargo trailer for a golf cart, wheelchairs, spare supplies and food, and we usually stay 3 weeks at Christmas and maybe a week or so at other times during the year. I believe the main use of the trailer is to carry Christmas or other appropriate decorations. We often rent a car for at least part of our stay to go get groceries, visit other attractions, pick up medications, or make a Wal Mart run.
You don't say what functions or services you may be in need of, but we have a motorhome to which we added a chair lift for the five steps to the main floor. The FW premium sites are wide and paved, and the preferred sites have smaller concrete pads, but adequate for most needs. Due to rehab of one of the boats, some boats to the MK cannot take wheelchairs. I don't know when the rehab is supposed to be completed, but there could be some delay waiting on the larger launch to the MK if non-transfer wheelchair access is needed. There was mention of space at the front or back of the launch for wheelchairs, but there is also space in the middle for 4-6 wheelchairs and/or strollers.
Trails End is accessible by ramp for the Hoop Dee Doo Review and for the buffet and take out, and The Backyard BBQ is ground level with paved access. The campfire is awkward due to the gravel ground cover, but can be accessed with some assistance.
We never drive to any of the parks but ride the boat to/from MK, and on to EPCOT by monorail. Internal busses take us to the Outpost where the park busses take us to AK and HS. All the newer busses handle three wheelchairs, so that is rarely a problem since we only have three wheelchairs right now. I don't know your specific situation, but we find both the internal FW busses and the park busses to be a very convenient way to get to the parks and back, and leave the driving to the "fellow" up front.
We usually stay in the 200, 1400, or 500 loops, all of which are fairly convenient to most facilities and activities. 500 is primarily a pet loop, but you might see pets in all loops these days, and of course your service animal can stay and go anywhere. Check out the Google site map on a sticky at the top of the camping forum for more detailed information on loop and facility locations.
We often walk to the Settlement/Marina area with the wheelchairs, but since DW had back surgeries this summer, she drives the GC with one wheelchair on the back and I push the others along the wide and very available sidewalks. If we're going to AK or HS, we ride a yellow line bus to the outpost to catch the appropriate park bus. We also usually use the GC for the laundry and the trading posts depending on our site location. And the GC is very handy for looping, especially around holidays, during which there are also colorful GC parades.
And most of the time we don't feel all that "old".
