Yeah, that book that Kodama recommends is great (I have the older version). I would strongly recommend heading southbound, unless you enjoy headwinds.
As you will see in the book, there are ample and lovely campsites on the coast, the state parks have hiker/biker sites which are cheap, beautiful, and allow you to meet and befriend the many other riders along the way.
Don't miss the cheese factory at Tilamook, make sure to sample the ice cream.
I did Vancouver Island to the Crescent City, CA, and have also done Astoria to Portland... no problem to just head up the main highway from Astoria to Portland, it is actually pretty pleasant and safe. There is also a prevailing west wind that blows you nicely up the Columbia River.
My route was along the east side of the Olympic Penninsula (to visit a friend in Port Orchard), then accross the peninsula to join the coast route. I did it in August 2003, had great weather, but you could also see some rain, I would be prepared.