Well let's take this one at a time since I just responded to your Minnie Van question:
1. The Handicapped Accessible cabins are in specific loops if memory serves with several in either 2600 or 2700 but there may be others spread around the remaining cabin loops as well.
2. The walk to other areas of the Fort can be long depending on your destination (the Fort is one mile in length) so on sidewalks that might take 20 minutes or longer at a reasonable pace. There are internal busses that travel through the Fort (two of the three bus lines run down through the cabins) and bus stops are every 2-3 loops apart or so. So my approach would be to go out of your cabin loop along the sidewalk to the nearest internal bus stop and catch a ride there. The busses have a ramp at the rear door in the middle of the bus and the front door near the driver can also kneel down lower to the road surface.
3. The golf carts are a standard 4-seater with front- and rear-facing seats. Disney has a few 6-seat golf carts that are about $20 more a day but can't be reserved separately (you don't reserve a 4-seat or a 6-seat, just "a cart"). If you reserve a cart and want a 6-seat, you can inquire when you pick up your 4-seat if a 6-seat is available. If it is, they will swap you out and charge the difference. If it is not, you can be put on waiting list for when one becomes available (if it does).
4. You say you've done Disney many times. You probably know the layout of the cabins is a queen bed with bunk beds in the back bedroom and a sleeper sofa in the living room (claims to sleep two). So your math works especially if the 5th or 6th person is only there a few nights and not the whole trip. Also, some people have qualms about 6 using one bathroom (getting ready in the mornings, yada yada). Mousekeeping will bring you extra towels if you call and request, that's not a problem. But if you have 6 max in your party, that generally triggers a suite or two rooms in the other resorts which can get pricey. And the cabins (a point we loved) have a fridge and stove plus microwave so we can cook some meals or eat a simple breakfast (and you have a charcoal grill and picnic table) so you don't have to pay for Disney swill at every meal for every person. You can control your food costs to some degree.
I'd say your plan works if the six of you can get a long for a short while and you aren't all Type A go-go-go types. A five minute wait for a bus can seem endless to some folks who post on here about the Fort. But it can work - some of these issues you would have even if you were at another resort.
Bama Ed