There are two "guaranteed" booking categories at OKW. They take the same number of points. Near Hospitality House (main check-in area) category includes bldgs 11 to 14 and 23 to 26. And then the other category includes the rest of OKW.
The self serve mug refill station is at Goods to Go, the snack bar located near the main pool. You can also have them refilled at the Turtle Shck, but it is not self service. Turtle Shack is a seasonal, limited hours snack bar near the Turtle Pond pool.
There are 4 pools located thoughout OKW, each with sandy childrens play area and hot tubs. There is a small sauna located in the base of the lighthouse near the main pool.
If you will be using Disney transportation, there are 5 bus stops located throughout OKW. They are,in the order of service, Peninsular Road, South Point, Old Turtle Pond Road, Miller's Road and Cove Road (Hospitality House).
Remember that only 3 buildings, 62, 63 and 64 have elevators, and they are often used for people with mobility issues, so you may want to try for a first floor villa.
As far as actual "best location" it is all subject to personal preferences. I like the Turtle Pond area, as well as bldgs 45, 45 and 53 to 56.
Here is an OKW resort map.