Hi Phil - and welcome to the Forum! We have lots of experienced poly folks here who are generally helpful and friendly, so please do not hesitate to post any thoughts and questions that you may have.
While the idea of a couple opening up and adding a third who will date both the husband and wife seems to be the most common public perception of poly, in reality it is the rarest and least stable of all poly configurations. There are a few reasons for this - one being that individuals willing to be that third are so rare that they are referred to as unicorns, that is, so rare as to be virtually mythical. Although - most couples who are seeking a third are seeking a bisexual woman (the proverbial hot bi-babe), so it might be easier to actually find a bisexual male third. Regardless, there are numerous practical and ethical considerations as well. Of course, it doesn't mean that it can't be done - but it is more complex than it might seem at first blush. I highly recommend this intelligent and thoughtful article on the subject of adding a third:
https://davidlnoble.livejournal.com/176039.html
On the other hand, MFM V's in which the men are not romantically/sexually involved - but both date the same woman, are not unusual and have proven to be one of the more stable poly configurations - at least based upon the numerous discussion that have occurred on this forum. (A triad is the situation in which all 3 partners are all involved sexually/romantically together, a "V" is a situation in which the hinge partner dates each of the two "legs" but the legs do not date each other - although they know of each other).
However, the most common poly situation for a couple who has opened up is when each partner dates their own partners independently. My wife has a boyfriend (who is currently living in our guest room) and I have a couple of girlfriends (one ldr and one local).
My long distance girl friend lives up your way and I can tell you that there is a significant poly presence in Spokane. I know that there are a couple of sizable Facebook groups for the poly community in Spokane.
Here is my list of the best poly web sites - that you may find helpful.
http://www.polyamory.com/forum/showthread.php?t=108191
Again, welcome to the Forum!