Parking at Downtown Disney during the busy season can be a real pain. The parking lot fills up, especially at the Marketplace end anytime, and the Pleasure Island/ Westside in the evenings. The boat launches there only go to Port Orleans Riverside/French Quarter, Old Key West or Saratoga Springs.. they run from 11 am until 11 pm, if weather is cooperating. The waterways in Walt Disney World do not all connect, so the Sassagoula River, which is behind Port Orleans is not the same body of water as Bay Lake (behind the Contemporary), Seven Seas Lagoon (in front of Magic Kingdom) or Cresent Lake (between Yacht/Beach Club and Boardwalk). The monorail has 3 tracks--- 2 that go from the Ticket and Transportation Center to the Magic Kingdom (one is direct, and the other going in the opposite direction stops at the Polynesian, The Grand Floridian, the Magic Kingdom, the Contemporary and back to the TTC, in that order). The other monorail goes from the TTC to Epcot and back. There are busses from each of the Disney owned resorts that stop at DTD. They make 2 stops, one at Marketplace near Rainforest Cafe, and the other in the parking lot across from Planet Hollywood. The busses run from 9 am to midnight at the Marketplace and from 11 am to 2 am at the Planet Hollywood stop. There is NO bus transportation from ANY of the parks TO or FROM Downtown Disney... this is so guests who want to drive to DTD and park to spend time shopping and dining will have places to park their vehicles.
If you want to visit Boardwalk, you may drive if you like. You will enter from Buena Vista Blvd, turning either rt or lt, depending on the direction from which you are driving immediately next to the Hess Station (across from the Entrance to Disney MGM Studios). Once you make that turn, you will take the 1st left, and go through the Security gates. You will need to show a picture ID, and state the reason you are visiting. Then you may either valet park, or park on your own. If you want to visit from the parks, you may take the bus, or in the case of Epcot or MGM, you may either walk or take the Boat launch.
Hope that helps!