We just returned from the BWV in Jan - enjoyed every minute of it.
They have a great gym - muscles & bustles. ~3 treadmills, ~3 ellipticals, ? # bike or rower (didn't use them, think they had at least 1). Good free weights and weight machines. Small area to do mat work. Towels and water bubbler there too. You do not have to pay if you are staying at the Boardwalk. You won't mind spending a little extra time in the gym if you get a fabulous treat at the Boardwalk Bakery (cheesecake brownie is worth more minutes on the treadmill!)
The walking path to Epcot is at the ESPN end of the wooden boardwalk. Walk toward the Beach Club, past the gazebo, bear right over the bridge and the world showcase entrance will be right in front of you. ~5-10 min depending how fast you walk and if you have a loaded stroller.
The walking path to MGM (now Hollywood Studios) starts behind the Boardwalk near the pools along the river. Don't go over the bridge toward the Dolphin/Swan - the path is on the Boardwalk side (although you could catch the boat launch there to go to MGM in case you do

) The path brings you along the river, under an overpass then right to MGM. Its ~10-15 min.
I hope you love the Boardwalk as much as we did. Our kids thought the surrey bike was fantastic (they weren't pedaling!) DS had a blast in the arcade, DD loved the lobby, DH was in awe of the ESPN zone and I loved it all! Have fun!