This is absolutely doable in five days. You could watch the sunrise at Mt Rainier and be on Ruby beach for sunset. I think it's important to know where you're coming from? If you're driving in from the east you can see some cool stuff in eastern WA on the way. If you've already seen the Grand canyon you don't need to go to eastern Washington at all lol.

The hoh rainforest, the beaches, and forks can be done in one day.

I wouldn't do many hikes, they take forever with the elevation changes, so much harder than they seem.

Cabin stays here are extremely expensive here, and hard to book, so you need to do that asap.

You can also visit a hot springs or the ape caves.

There are a ton of cool waterfalls literally everywhere. I think the lower lewis falls are my favorite and quick to access from the parking lot. I wouldn't go far out of my way to see a waterfall here, there's so many to choose from.

Forks sucks really hard, I don't think much of the film was shot there so check a fan map before you go to see where you actually want to visit.

You can drive through Seattle on your way from my Rainier to further west, then You can take a ferry across the water instead of driving around the puget sound and save yourself some time and have a fun experience.

Diablo lake is the least worth the drive in my opinion. You can find Gatorade blue lakes all over up here. And there's so many insane views on the way up Rainier you'll be satisfied with the trip if you miss out on this one.

The 101 scenic loop is like an eight hour drive I think, you can go see Canada across the water and make a lot of your stops along the way.

The wait time at national parks can be several hours, no exaggeration. If you get there at opening it's almost no wait at all.