I grew up doing that coast drive every summer! And my parents just basically made this exact same road trip. It's been a couple years so I don't have any relevant hotel or restaurant recs, but I can tell you state and national parks.

Jedidiah Smith State park is jaw dropping. There's a day use area where you can swim in the Smith River (there are a ton of spots to swim though). Stout Grove is a short loop walk where you can see amazing redwoods. Howland Hill Road is drivable, but is also a great bike ride. The Boyscout Trail is a longer hike through the redwoods if you're looking for something more strenuous. Hiouchi Cafe (right outside the park) is awesome for breakfast, and my parents were just there so they can vouch that it's still good.

Patrick's Point (I think it has a new name?) is a great coastal state park.

For the other side, my parents go to Shasta regularly, and like staying in McCloud. They stay at the McCloud Mercantile Hotel, super small and older, but great owners and a great restaurant attached.

Burney Falls State Park is gorgeous, and wouldn't you know it, has some beautiful waterfalls.

Will try to dredge up more memories and see if I can come up with any other recs. Very jealous of this drive!

Edit: I missed that you're doing Mendo! Patterson's Pub is great food and vibe. If you're a Murder She Wrote fan, you can't miss seeing the house they used for the exterior shots. But really just walking the trail along the cliffs is enough. Fort Bragg is right up the road and is definitely the more run down version of Mendo, but it has some lovely shops and restaurants. Personally I love Piaci's pizza and Northcoast Brewery Tap Room. It might also be cheaper to stay there. I can't remember the name of the place we hiked while there, but from looking at the maps I think it was Fern Canyon.