I have ridden the California coast route several times in each direction. Aside from the usual headwinds on a S to N direction what I missed most was the ocean view easily visible when on the opposite side of the road heading South.
The inland route suggested above makes for a nice loop trip with lots of variety of terrain and climate.
My last trip was farther North. It followed the Klamath River route Hwy 96 to 299 and over to Arcata on the coast. The highlight section was the Matolle River road from Ferndale to Petrolia to Honeydew and back to Hwy 101.Steep grades but great scenery with few cars. You will enjoy any route but I strongly advise using a mirror to see what vehicles are approaching from behind you.