I'd guess about 10 in the current climate regime. I would say maybe 15 for the last 100 year average. SEA averaged 15.2" between 1945 and 1975. The Puget Sound area in general (areas near the Sound itself) averaged around 25" in the 1880 to 1900 period.

Yea as a general rule of thumb in King County I would say anywhere east of HWY 18 and East of Issaquah generally does better. In North King County I would say being east of Lake Sammaish and HWY 203 in Carnation is preferable. All of those locations are above 500 feet and closer to the mountains.

I think one of the most bothersome things about this weather pattern is the way the days just bleed into each other. One drippy day becomes exactly identical to the previous and the next. You almost lose track of time.

Probably low 10s. Being higher up even in the CZ doesn't make a huge climo difference compared to anywhere else in the lowland metro area, until you head out east and well above 500'. Samammish/Issaquah Highlands is where you start seeing annual averages greater than 20"

Can't speak much for the PS area but I know you can get some good Convergence Zone setups there, and you are at 500', I would have to assume you get at least 10" annually.