You should have a great trip, the area you are traveling to is beautiful.
If traveling on a Saturday going either way is OK.
SeaTac airport is south of Edmonds by 30 mile about 40 minutes in good traffic. Ferry runs every 1/2-hour; takes about 1/2 hour. Unless a 3-day weekend there will not be a long line. Ferry cost $11.55 one-way.
From Kingston it is about 61 miles to Port Angeles, takes about 90 minutes.
If going south from SeaTac on I-5 it is about 1/2 hour to the Tacoma Narrows Bridge. This bridge takes you over the south sound. Mileage from the airport is about 107, about 2 hr 11 minutes. The bridge is tolled when going west, cost $4.00.
Thus going north from SeaTac to Edmonds is longer.
You might make a round trip. SeaTac south around the sound to Port Angeles then back via the ferry.
There are many ferries going across the sound, the Kinston Ferry is just one. See link below.
http://www.wsdot.wa.gov/ferries/
If traveling back to SeaTac on a weekday during morning or afternoon rush hour would forget about the ferry/Edmonds and just drive around again.
Plan for rain, high about 45F, low about 32F.