Hall mosses and hoh river look fantastic! Would you recommend staying near Forks? And then driving back to Seattle to go to Vancouver?

Yes, you can stay in Forks. There aren't many options for accommodations on the west side of the Olympic Peninsula. Staying in Port Angeles is also feasible but it's a pretty long and boring ride (couple of hours) each way from PA to the Hoh visitor center or to La Push for the beaches.

If you're going to Vancouver after Olympic NP, then I wouldn't return to Seattle at all; just keep the car and use the Port Townsend - Coupeville ferry like I described above. You may need to find a hotel in Vancouver where parking is affordable (these exist) but the car would also be of value in any excursions from Vancouver, such as to Lynn Canyon or Grouse Mountain.

Right. So this is what I'm thinking generally:

Fly into Portland
Portland/Columbia River Gorge area
Return rental car & train to Seattle & get new rental car
Seattle
Drive to Forks (can this be done via bainbridge ferry as well)??
Hiking in Forks area/Lake Crescent
Port Townsend-Coupeville Ferry to Whidbey Island, drive Whidbey to Vancouver
Vancouver/Vancouver area hiking
Drive back to Seattle and return car


Does this seem logical/doable? Am I missing anything huge?
Also, how would taking the bainbridge island ferry to port angeles work? I've never used a car ferry before!

Thanks!

Day 1: Fly into Portland

Day 2: Portland

Day 3: Portland

Day 4: Portland

Day 5: Train Portland >> Seattle >> Port Townsend via Bainbridge Island ferry >> Forks

Day 6: Forks

Day 7: Forks

Day 8: Port Angeles

Day 9: Port Angeles- Coupeville ferry to Whidbey >> Vancouver

Day 10: Vancouver

Day 11: Vancouver

Day 12: Vancouver >> Seattle

Day 13: Seattle

Day 14: Later flight Seattle >> Chicago

Day 5: Train Portland >> Seattle >> Port Townsend via Bainbridge Island ferry >> Forks

Port Townsend isn't on the main route between Seattle and Port Angeles/Forks.

Assuming you want to visit one of the La Push beaches as well as the Hoh rainforest, I'd reduce the number of nights in Forks to just one, something like this -

Day 5 - Portland - Seattle - Port Angeles
Day 6 - Port Angeles - Hoh valley - Forks
Day 7 - Forks - La Push - Port Angeles
Day 8 - Hurricane Ridge or optional one-day visit to Victoria, overnight PA
Days 9+ - as planned.

Thank you for your help! I think I have it figured out.