Thanks for the info; I may need to plan four or five days on the coast! I had thought about hitting the coast around Lincoln City, spending a night in that area, and then moving on to the Newport area for a night or two and ending the coastal trip near Florence. If I try and start at the Cannon Beach area, Im likely going to need to add a couple days to the trip dont you think?
Cannon Beach tends to have "MORE" shops, restaurants, etc. simply because it serves the PDX area. Plus they have some nice beaches. In the summer it can be pretty crowded, but after Labor day things slow down quite a bit.
If you cut across on HWY 18 to Lincoln City you'll go through some really nice wine country. Allison Hotel in Newberg is very nice great food. Owned by a former client of mine. I'd continue on from Lincoln City to the Sylvia Hotel rather than stay in Lincoln City. Might consider the River House in Florence, it's in old town, a number of shops etc. Not on the beach but should be decent.
Also, September can be great weather on the coast. It's one of my favorite times of year to go to the Oregon beach.
It's hard for me to say how long to spend on the coast. It depends on what you like, if I'm going to the beach, it's usually for a couple days, 2 or 3, at one location. Walk on the beach, hit some art galleries, enjoy some good sea food, and just relax.
Note: Sylvia Beach Hotel could likely be booked already. If you're considering it check NOW.
Note 2: These are "two lane roads" for the most part, with some passing lanes. If you are a very aggressive driver, I'd stay away from the coast all together. It's not a place to hurry. That goes for the roads from the Valley to the coast and along the coast. Good news is most of the California RVs are off the road after Labor Day.