Regarding crossing the Yukon River by ferry at Dawson...if we're going westbound over the Top of the World, we'll overnight at the Yukon River gov't campground on the west side of the river. Then we can leave whenever we wish the next morning without thinking about the ferry.
As well, the paddlewheeler graveyard, which is a short walk north of that campground, is an interesting site to explore.
There are no services at the Yukon River gov't campground. If you get there early in the afternoon chances are you'll get a nice site by the river though, which makes for a pleasant evening around the campfire.