There is no bus time schedule listed anywhere. Typically its about every 15-20 minutes. During peak times of the day it can take a bit long sometimes. I have stayed on property at WDW 5 times so far. 3 times at All Star Movies and 2 times at Port Orleans Riverside. During those times I think maybe we had 2 or 3 times where there was a 30 minute wait for a bus. I love the bus system and would never stay outside the park except for maybe if the hotel was free.
There are 24 resort hotels at WDW. You can walk to the MK from the Contemporary (we've done it twice). From the Boardwalk, Yacht Club & Beach Club you can walk to EPCOT. You can also from the Swan and Dolphin, but yo have to walk through either the Boardwalk or the Yacht Club & Beach Club resorts. There are no resorts you can walk from to either Hollywood Studios or Animal Kingdom or Downtown Disney. Same is true for either of the water parks.
Disneyland Resort occupies 500 acres of land with 2 theme parks, 3 hotels and a Downtown Disney area.
Walt Disney World Resort occupies well over 30,000 acres of land with 4 theme parks (Animal Kingdom itself is 500 acres), 2 water parks, 24 hotels, a Downtown Disney area, ESPN Wide World of Sports Complex, Disney Quest, 8 golf courses and several additional recreational activities.