There is very little transport between resorts. The exception to this the MK resort (GF, Poly and Contempory - and possibly Wilderness Lodge if you catch the boat from MK), and the Epcot resorts (Yacht and Beach Club, Boardwalk and Swan/Dolphin). The only way to resort hop the other resorts is by car or via going to a park and then to the resort.
I think you can park at the resort, but you may be given a short stay parking pass or asked if you have a PS reservation at the resort restaurants.
You could park at Downtown Disney and then get the Disney bus to the Poly. From there you will be able to travel to the GF and Contempory. Then from MK to Wilderness Lodge. You can then catch a bus to Epcot and walk through the international gateway to the Boardwalk, Yacht & Beach Club and the Swan/Dolphin. You can then catch the bus back to Downtown Disney.
You may just be able to do this in a day!
Another option if you want to see some other resorts is the DVC tour. You can sign up for this at any DVC booth and you get a tour of the DVC resorts and I think a free lunch! I'm told there is no hard sell.