Absolutely take the bus to MGM and then walk to BW. When you get off the bus, keep walking toward the canal, with the park on your left. Go to the right of the canal, you will be on a walkway, with the parking lot on your right, canal on the left. The walkway will go down a slope, towards the water. Stay on it, go under the bridge, then you'll be at BW. You can cut through at the main pool area (clown pool!!). Cut through there, go underneath the building, with the health club/arcade on your right, restrooms on your left, you'll be at the village green, with the boardwalk to your left.
Or, you can stay on the walkway to the end, then go right, with Jellyrolls on your right, Atlantic Dance Club on your left, onto the boardwalk.
This is one of my favorite walks in all of WDW. It takes about 15 mins.