Another travel question road trip Washington state

Thank you for all the great suggestions. Struggling with fitting it all in. I think we will have 9 or 10 nights in addition to the time we will spend with our friends.
The only nonstop flight from our airport gets to SeaTac at 445 pm.
Do we head to Seattle or out towards mt Rainer or straight up to cascades? I also am struggling with how many nights in each location and where to stay on the cascade loop. I don’t want to be moving every night. Also is Whidbey island worth a few nights? Should we skip Mt Rainer and concentrate on Cascade loop?

Another thought is to fly to Lopez island on Kenmore Air and pick up rental car in Anacortes after our stay on the island.
Appreciate any thoughts on my ramblings.