If you haven't been to the NW before you may be surprised at how BIG the states are. That was the one thing I kept forgetting when I was back east, how small the states are in comparison. You can certainly drive all that, but the Redwoods/Crater Lake are about 17 hours drive time (no stops) SW from Yellowstone.
The Olympic peninsula is about 9 hours drive time (barring any traffic through Portland, Tacoma, etc) straight North. This requires leaving the coast line and driving up I-5. If you plan on taking Hwy 101 don't plan on averaging more than 40/50 miles an hour. There are a lot of turns, a lot of small towns, and a lot of traffic. It is a surprisingly long drive. Beautiful like nothing seen on the east coast, but long.
The Oregon/N. California coast line is vastly different the N. Washington/Olympic. They are both great in their own rights. But vastly different.
As many people suggested, you could make two great 2 - 3 week vacations just either along the pacific coast from the San Juan Islands to the Redwoods. Or along the continental divide between Glacier and Tetons. I would almost choose between one of those two depending on time of year and personal preference for activities.
