I suggest Sitka Alder, You probably already have it on your property if it's rural.
NW
native, even the leaf litter contains a high amount of N.
I am 20 miles SW of Corvallis, thinking along the same lines. my list for N-fixers
Sitka Alder, Siberian Pea, comfrey (ground Cover) and
black locust ( for the wood),
maybe Goumi and autum olive if I can find one with decent fruit.
Cheers!