https://www.google.com/maps/dir/King...47.5232072!3e1

This is the route I would take. I haven't ridden it yet but I have walked it and it is fine. It is a bit industrial around the docks before hitting the trail over the West Seattle Bridge but nothing to worry about. You'll be on a dedicated path until you hit West Seattle and then there should be bike lanes all the way down to the
Fauntleroy Ferry over to Vashon. If you have any other questions, let me know. I'm still new out here (only have lived on Vashon or in Washington State for that matter since last July) but I'd be happy to help!