Its an older thread you have your plan already. I go down to Portland every so often for a football game. Not NFL real football Portland Timbers are our local rivals. Its friendly we go have a beer with Timbers Fans. I wander around Portland quite happily it's a friendly place.
Went down the Coast to Eureka in August. Don't worry about it. We stayed in cheapest motels all were fine, Some right in middle of some towns might have a few homeless. None we were worried about. California and the Redwoods are nice but I Love the Oregon Coast. You can't go wrong, When you are in the Mountains. Columbia Gorge spectacular.
There are no bad routes. They are all good rides.
I prefer to avoid the I5 it can be very busy and boring. Lots of really cool small towns on the coast. Camping books up early at peak times and is busy.
Camped at Cape Disappointment on our first night. Arrived after dark, Got up early complaining about the traffic noise. It was the Surf.