I am at WL as well, but WL won't hold five people (unless you book the deluxe CL rooms $$$) or a two bedroom villa at VWL (also $$$).
Any of the monorail resorts would be convenient. Poly actually has the most transportation options, because you can walk to/from the TTC, so the express monorail and ferry boat are also available to you, in addition to the resort monorail and Poly/GF boat.
I love FW, but you would be taking a boat from MK to FW, then unless you rent a golf cart, taking the internal bus back to your cabin. I don't mind using the internal bus system, but I've never gone to a late night party while staying at FW so I don't know if that would impact your choice. Another thing to consider is that September is the peak of hurricane season and the Fort is evacuated if there is any storm headed toward central Florida. I usually don't recommend people staying at FW in September because of this.