Day 5-6 may be combined. After visiting N Cascade, you can cut Hwy 9 N to Hwy 542. I also recommend going further East on Hwy 20 to Washington Pass, time permitting. It is a very dramatic view at the Washington Pass rest area (short walk to a high point). Don’t know how much snow will be left at Washington Pass in August. But the view should still be good regardless. I am not sure how you get from Sumas to Richmond though.
Day 13: I assume you’ve checked the Orcas Island ferry schedule. I think you should spend this night in Anacortes as Bellingham is going opposite direction. If you get to the Anacortes Ferry terminal early, you may pleasantly kill the time at Washington Park (out of the ferry terminal, right turn into the park). Take the one way scenic loop drive. I was there today for the Nth time.
Day 14: You need more time for Olympic National Park. That appears very tight… You don’t need to drive to Olympia either. Should continue onto Astoria on 101.
Day 15: Again no need to drive to Portland (see Day 14). If you must overnight in Olympia, I would get off I-5 onto Hwy 4 going east in Longview. You don’t have to go all the way W on Hwy 4 (unless you want to cross the Astoria bridge). There is small ferry you can take crossing the Columbia River somewhere on Hwy 4 (forgot the name of the town). But again, I don’t understand why you are driving back to Portland.