Generally, driving down 101 is a quick and easy drive. You’ll have lots of places to pull over and take photos and little things to do. Be sure to hit tourist information centres along the way for useful coupons to some of the attractions in the area.
The Sea Lion Caves are wonderful and worth the couple of hours to do it.
Here is a nifty link to a few things to do whilst driving down the Oregon Coast. The Prehistoric Gardens, whilst a bit cheesy, is fun and a very nice walk through dense fern growth and huge trees. I like it…
From Brookings, the next “big” town down on 101 is Crescent City - about 15 miles. There, you will find an Under Sea Adventure touristy thing that has a touchy tide pool, petting sharks, and lots of fish. It has been there since before I was born - yonks ago - but if that is the kind of thing you like… There is a wonderful drive around there though through the redwoods. The area is Stout Grove. Easy to find, but feel free to email me for directions if you’d like.
Klamath, where you’ll find the Drive-thru tree, is another 15-18 miles south. Just before the tree, there is the Trees of Mystery - recognisable by the huge Paul Bunyon and Babe. They make the most brilliant homemade fudge in tons of flavours. There is also a Native Indian museum there (free) with tons of local stuff.
Back North, Tillamook has a lovely cheese factory.
Bandon has the cranberry candy stores and items. Lots of touristy shops to buy goodies and prezzies.
As for the idea of the Avenue of Giants and Crater Lake, unless you want to add a few days onto your journey, stick to what you have planned. Eureka* is an hour and a half (if you’re a lead-foot and know the roads) from Crescent City. The mansion isn’t all that interesting and has been turned into a Gentleman’s Club, so the most you could do is drive by and gawk. I’ve photos is you want to see the horrid green building. Avenue of the Giants is about 4-5 hours further South - though impressive and quite enjoyable. Crater Lake is fantastic (used to work there), but would require a day out of your itenerary to see it. Believe me, it is definitely beautiful, but something you need to plan for. Also, in October you will hit a bit of snow going up the mountain. Not fun if you aren’t used to it and the 10 MPH corners are bad enough on a clear day, let alone with snow.
*If you do decide to go down to Eureka, I most highly recommend eating at the Samoa Cookhouse just outside Eureka. Great food, fresh bread, very friendly staff. Worth the visit.
I hope you enjoy your trip.