Someone else already mentioned the wait time to get into Mt. Rainier. Typically I recommend people get into the park before 7am or the traffic will back up for a mile or more. If this happens, turn around, go to Skate Creek Rd. which you just passed and hike to High Rock Lookout (assuming you have a sunny day). Then enter the park in the evening after the traffic has dissipated. Hopefully you're staying inside the park for the days you're there.

Another thought, a lot of the parking lots for the popular hikes are very small. From personal experience, this is very true for the Marymere Falls trail/Mt Storm King trail since they both leave from the same parking lot. If you do get a parking spot there, I'd recommend doing both hikes the same day. Marymere is pretty but not that spectacular.

Comet Falls in Mt Rainier NP has the same issue with only 15 or so parking spots. You can either rely on luck to get a spot or arrive there really early (like before 7am). If you do Comet Falls, hiking on from there up to Van Trump Park is epic. You'll feel like you're standing on the mountain itself in an alpine meadow surrounded by wildflowers.

My sister had this happen. She took it to court but ended up having to pay the whole fine anyway.

That's true but it sounds like OP wants to explore and get a good experience of western Washington and I think hwy 101 will do that better than just a straight drive up I-5. Though it kinda depends on how long their trip is.

Sure thing! I hope you enjoy your trip here!

I wouldn't recommend Seattle unless you enjoy big cities. However, I've taken a ferry from Seattle to Victoria (British Columbia) and had lots of fun. Or, you could look into taking a ferry to San Juan or Orcas Island north of Seattle. I guess it depends on your budget and how much time you have.

If you're sticking to the main highways, any type of car will be fine. If you plan to go into the mountains, you'll likely need tire chains regardless of your vehicle.

I'd recommend driving up highway 101 around the peninsula. Olympic National Park and Lake Crescent are beautiful anytime of the year. Mt Rainier is a great park but look ahead to make sure it's open and if tire chains are required. Ashford, right outside the Paradise entrance is a good town to stay in. And not too far away you could visit Northwest Trek Wildlife Park to experience PNW (Pacific North West) wildlife.