Driving only 4 hours limits where you end up spending a night.
If you want redwoods and coast, my suggestion would be:
Day 1: SF->Mendocino via 101 (inland) then 128 thru the Anderson Valley to the coast, then CA1 to Mendocino.
Hit a winery or two in the Anderson Valley, and/or stop at Anderson Valley Brewery for some craft beer. Enjoy the evening hitting the shops and restaurants in Mendocino
Day 2: Mendocino to Klamath. I'm not a big fan of either Eureka or Crescent City... but then there aren't a lot of options in Klamath. Book early of you want a B&B or a motel in this area.
Tour the Redwood Parks upon arrival or next morning before leaving.
Day 3: Klamath to Florence.
Enjoy a leisurely trip up the southern half of the Oregon Coast.
Day 4: Florence to Astoria.
Same as last day, but spend some time exploring Astoria and surrounds.
Day 5 Astoria to Seattle.
These days run from 3 hours to 5 hours driving time (plus stops). I suggest you poke around a bit to see if Mendocino and Astoria look like interesting places to spend a night (I suspect they will).
There are other options heading north that avoid the coast, but offer up sights like Crater Lake, Portland/Columbia Gorge... but on your schedule you'll have to pick which option most appeals to you.
In month or so I should be posting results of this trip; you may want to check back then as it overlaps some of the territory you'll be covering.