@indyfabz : Thanks for your advices. Maybe we'll take a train to enter and leave the cities. We think to use warmoshower, couchsurfing and hostels.
We definitely want to go to Glacier NP and spend a few day there. What is the weather there, in september ?
Excited about the ferry ride too, do you have the name of the hostel ?
According to locals I have spoken with, they love September in Glacier. The bugs are gone as are many of the crowds. Apgar, Sprague Creek and Avalanche Campgrounds, all on the west side of the road, have hiker/biker campsites. A visit to Lake McDonald lodge is a must on the west side. Grab a beer at the bar and enjoying it down by the water.
I would check the park's web site. There has been an ongoing road rehab project in the park. In past years, the park service has closed portions of Going to the Sun for periods in September to allow for uninterrupted constrcution work. Later in the year they will likely post closure information on their web site.
This is the site for the HI Hostel in Seattle:
I think there are a couple of others. The HI Hostel was packed in late May. Don't know how busy it is at other times, but a reservation is probably advisable.
This shows the ferries:
It's been a long time, so I don't remember the exact ferry that took me close to the ACA Pacific Coast Route, but I am pretty sure it was either the Bainbridge Isnand or Bremerton ferry.