The cabin loops are grouped towards the outpost. The outpost is where you check in and the entrance to Ft.W.
The Settlement, where HDD, Trail's End, Crockett's Tavern, petting zoo, marina(boat to MK) is at the other end of Ft.W.
Meadow's Trading Post, pool, bike barn and campfire/movie are in the middle.
There are 3 bus routes at Ft.W. The orange bus runs from Outpost to Settlement and back. You will probably never need to be on an orange bus.
The yellow bus and purple bus makes loops throughout Ft.W. To go to MK from the cabins you take Purple bus to Settlement and then walk a short distance to the marina and take boat to MK. This is the same route to catch bus to MGM.
To go to Epcot, DTD, TL, AK, you take Purple bus to Outpost and then transfer to the respective bus.
The buses come quite often and we never had a long wait. Keep in mind that during HDD times the buses and boats are often more crowded.
Because we have a big famiy and 2 in strollers, we end up driving to all the parks except MK. It is just easier for us to hop in the van and head straight to the park. Even better coming home from TL - no riding a bus in a wet swimsuit.
The cabins are wonderful. Check out the "Camping at WDW" forum on the Disboards - tons of great info.