Buy this book (I have listed the Amazon.com link because that is what I found first, not because I am shilling for Amazon.com).
http://www.amazon.com/Bicycling-Paci...5906023&sr=8-1

This should tell you just about all you might want to know.

Also, is there any possibility of riding Seattle to SF? You are far, far more likely to have near-constant headwinds going south-to-north than the other way around. Constant headwinds = no fun.

Is it dangerous? Can't speak for Oregon or Washington, but roads in California require that you pay attention. Hwy 101 ranges from full freeway (more than ample shoulders but lots of fast traffic) to some two lane stuff with narrow shoulders. Mostly, there will be adequate shoulders.

Hwy 1 will usually have little to no shoulder. Most of the time, the lane is wide enough and/or the road is curvy enough and/or traffic is light enough to make coexisting with cars and trucks manageable. One suggestion - do not ride Hwy 1 between the Pt. Reyes area and the Golden Gate Bridge. The combination of narrow, twisty roads, lots of San Frqanciscans driving driving to and from Stinson Beach and significant uphills make it too dangerous IMHO. Go inland through Samuel P. Taylor State Park, Fairfax, Corte Madera and Sausalito instead.