totally understand wanting to have an adventure, be out of your comfort zone and all that, but given your traveling experience and using common sense, there's every reason that this will be a fun trip.
I can't comment on the Washington State part as I never did it, but as the others mentioned about campgrounds etc, you'll have to look into the logistics of where towns are, campgrounds etc etc and plan accordingly.

You will want to inform yourself about wild camping in that area re bears etc and again, use common sense and commonly practiced safety stuff like not having food in your tent, hanging it at least on a tree nearby or whatever. Generally that's a big advantage of a campground, as they will have bear and animal proof garbage cans, this stops bears from learning that they can wander in and get stuff easily. Around here also there are lockers to put your food into, but the "no food in tent" rule is always going to be important to follow.
Don't forget also that having food in your tent can attract little critters like mice, bigger guys like raccoons (if they have them on the west coast, I forget) but even mice can be a real pain in the arse as they can chew a hole in your tent to get to food, et voila, a holey tent....
Re distances between towns or stores, I've always found it good to have some sort of "emergency" food in the bottom of a pannier, a can of tuna, some pasta or whatever, something to have if for some reason you can't get to a store.

the "Riding down the west coast" type books or whatever will give you lots of info on all this stuff, and then its so easy with google maps, streetview and stuff to see what stores, campgrounds etc are available where, and it will be fun for you I'm sure to start doing "Plan A" hopeful distances per day and where you'll end up each day.

I probably did say this, but especially as you are 6'6" and a big guy, really get your wheels checked out for spoke tension and if the bearings need regreasing etc. If you are a lot heavier than your last trip, you really want to make sure your rear tire is up to the trip, and much better to get this assessed long before the trip--just in case you end up needing to find a stronger rear wheel or something.
The trick is to find a really good bike shop with mechanics who know touring.
I suspect you are a heavy fellow, so even more important to get your wheels expertly assessed for your weight, plus maybe another probably 40lbs of gear.

Using both front and back panniers is always going to help distribute weight, making life easier for the wheels and reducing the chances of having busted spokes on the trip, which frankly is a real pain in the arse.
Wider tires can help with cushioning the blow going into your wheelset, I used 2 inch tires when doing my Latin America trips and even though I only weigh 135, I was riding on rough roads a lot, so having the wider tires at the right pressures for my bike weight really helped my wheels not have problems.
You'll be on paved roads the whole time, but I still wouldnt use less than 1.5 or even 1.75in tires.
What size wheels does your bike have? There are lots of good tires available for 26in wheels (my bike) or 700c, but no matter what you have, having new tires for the trip is always a good idea, and by doing training rides with all the crap you'll be carrying, you'll get to know what pressures to use for your specific weight.