1) June may be a bit too early to cover Pacific NW NPs - some areas may still be covered by snow and roads still closed - you need to NP site to check out each park's info.
2) Last August we did a grand circle - based on Wunderlust's suggestions and our ability (driving long distance, for example) we mapped out our routes that covered Crater Lake from OR (quite a bit out of the way), Mt. Ranier, North Cascade, Mt. Baker, Olympic and San Juan Islands and some OR coastal areas too. The total time involved are 8 days but were separated into 2 portions with 7 days stay in Vancouver in the middle.
We did Crater Lake first thing, then drove North. On our way Up to Vancouver, we did Mt.Ranier, North Cascades, Mt.Baker. On our way Down from Vancouver we did Olympic, San Juan Islands and Oregon Coast.
The trip was designed not to repeat our routes. After actual travel, the conclusion is it is better to do some backtracking instead of avoiding repeating as some areas have not much to see but added lots of driving, while certain "essential" areas are concentrated enough that backtracking is worthwhile (in order to go back to I-5 area).
3) If you really want to cover Crater Lake NP, you may be better off to consider flying into PDX instead of SEA. The drive between SEA and PDX isn't bad. Another advantage is, rental car cost is much cheaper at PDX than at SEA. We took our car out from Budget Portland city location and returned to Portland airport location. 2 weeks rental was $220 incl all taxes. Dirt cheap. Identical car class if rented in SEA was $450! We did not buy insurance but relied on our Signature Visa card. Knocked on wood, nothing happened. (Unlike our Yellowstone trip in Sept '05 that we had to invoke Mastercard coverage due to hailstorm damages.)
4) All our lodgings were done with Holiday Inn Express, except one night at Portland where we pricelined downtown 4 star and lucked out with Hilton. The reason we used HIX mainly because we had pts to spend. This approach added some extra driving time (may be 1 to 2 hours on some days).
5) You are welcome to ask away when you have better ideas of your upcoming trip. Just keep in mind I will be away from late March to early May (going to NZ and Australia).