NW, like up near Bellingham? Or NW meaning Oly Peninsula?
Zones aren't really going to matter, though if you are talking fruit trees in WA. You are good there.
I'm still thinking of the pine trees and your .25 acre. *Nine* on a .25 acre? What kind are they? Are they pine trees (like native shore pine--good choice for Western WA) or "pine" trees (something people call all manner of conifers, including Douglas firs which easily get to 100 feet in short order.)
I'm still less concerned about soil acidity than I am with crowding, which is why I ask these questions. WA soils are naturally acidic, but not intensely problematic, even with needles on the ground.
If these are shore pines, you should be pretty good to try what you are thinking of. Anything larger (and shore pines can get pretty big), I would try to find a better spot. Because of crowding, both above ground and below, not acidity.