For a 6:45 adr, I would to EPCOT or DHS and then transfer to the AKL bus. Figure on it taking at least an hour. I would leave AoA by 5:30....maybe a bit earlier. I love to poke around this resort, so if you get there early, you can check things out.
You can really take the first park bus that comes, and then transfer. But, MK is further away, and AK is okay as long as the park isn't closing.
Two good options. Take a bus to DHS. Then you can walk to YC....takes about 15-20 mins. Or take the boat if it's at the DHS ****, or just coming in. Otherwise it could be a lengthy wait.
A cab isn't a bad idea. The cost should be around $10 or so...it's less than a 10 min drive.