It sounds a fantastic route, but I’ve no personal experience of cycling it. The coast is actually pretty remote. You might find that distances between any habitation in some places are quite large, are you thinking of camping or hotels/motels or a bit of both? If you go late summer (July/August) it might be worth keeping an eye on State Park / National Park campsites if you hope to use them, as they can get booked up particularly at weekends.
If you go early summer (May/June) you stand a very good chance of seeing the grey whale migration back up north, they come in to about 1/2 mile from the coastline.
As far as I know, the only bit of the 101 away from the coast, which is also a dual carriageway (south of Eureka), has a paved road adjacent which you can cycle through the Humboldt Redwoods State Park. Have a search for similar off-road trails in other parks and reserves, because they tend to be paved in the USA.
Doing the route from north to south, towards the end, you could head inland to Calistoga or Sonoma to the hot springs as a nice detour, with a lovely run in to SF via the vineyards in Napa or Sonoma valley.