Re: Boardwalk Transportation
If EPCOT is closed, then no you cannot walk from the BW to the monorail. When EPCOT is open it's not a bad walk at all. We've done it plenty of times.
The buses are pretty full for that particular circle of resorts, but you are going to have to use them if you want to travel beyond DHS or the monorail options.
The monorail to EPCOT is out of the TTC so MK doesn't really have a bearing on that. And usually MK is open longer than (if not as long as) EPCOT. EPCOT almost always closes at 9 or 10 depending upon the time of year, whereas MK can be open after midnight (again depending upon the time of year).
You can walk from BW to DHS, or take a ferry. Same for EPCOT as you know. Walk or ferry. AKL you'll need the bus, same for DTD.
MK is the walk through EPCOT to the monorail method, or take a bus. Downtown Disney is a bus.