That is one possible route, but consider that the bus drops you off in the front of EPCOT. You'd have to walk all the way to back, then exit through the Intl. Gateway to walk to the Boardwalk. This walk can take 20-30 minutes, depending on the crowds.
I'd probably take a bus to MGM, and ride the boat over from there to Boardwalk. It would probably take about as long, or maybe slightly less time, but at least you won't have to do all that walking.
Also, this route saves you the time/hassle of having to enter a park (EPCOT) on your way to Boardwalk. You just get off the bus in front of MGM, and walk over to the boat dock without having to enter MGM.