When we visited Olympic NP, we stayed in a nearby campground as a base. Each day we'd pay attention to the weather reports and plan accordingly. On a rainy day, we went to places in Port Angeles, saving the trip up Hurricane Ridge Rd. when the mountains weren't fogged in and covered with clouds.
I suggest you do the same, base camp and take daily trips from that location. I can't talk about the ferry, I don't know how busy it is and if reservations are the only way to get aboard. Just try to be flexible, especially in the NW.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI