Roadtrip in PNW ( first time EVER in the US )

Hello everyone! My fiancé and I are planning our first trip to the US for our honeymoon in October next year. I am from europe and it has always been my dream to visit america’s beautiful nature. There are so many places I want to visit but we will be starting with the PNW. Our plan would be to fly into Seattle and roadtrip around Olympic Park and go down to the Oregon coastline if possible before driving back to Seattle. Ideally, we’d like to also visit Mt Rainier. We aren’t big experienced hikers, so we’re not planning on doing day long hikes or camping overnight. but we’d like to enjoy as much as possible in 10 days. I’ve seen on social media people saying that it’s so full and telling tourist not to come, that it’s impossible to get an hotel or get into the parks ( not sure what that means, do we have to make a reservation ??)

Any suggestions for our itinerary?

Also wondering, which neighborhood in Seattle and around would be good to stay in for the last couple of days of our trip ? Our goal being the roadtrip mostly, we’d probably shop a bit and try out a few local food in Seattle too before leaving. I also really love seasonal home decor and want to go to stores Marshall’s and Homegoods, and i could be wrong , but for some reason they seem to be kind of outside the city? Would we need a car in Seattle to move around and shop to these places ?

Another of our option would be to stay in Portland, Oregon instead of Seattle ( only going in and out Seattle airport ) how would that be?

Thank you everyone who reads this and comments :)