Heh, too much here to address now - my brother's in town from Sitka and heading back tomorrow, and there's Irish Whiskey involved now!
OR has an income tax. For businesses, there's a Metro tax for those in Multnomah/Washington/Clackamas counties (I'm in Multnomah). Also for businesses, there may be city taxes (Portland and Beaverton do). For businesses, you may or may not be able to work out a "break" or "moratorium" - manufacturing businesses that employ people like Intel or Nike get breaks, small businesses like mine get shown the back shortcut to the door, which is why we're looking to relocate now.
WA has a sales tax, and no income tax. WA residents who work in OR pay a non-resident income tax - and have to deal with the clusterf*** of the limited access from one location to another because of the bridge-bottleneck highway system (keep in mind here that I'm from NYC). Clark County has a county tax, levied on top of the state tax. Vancouver has a city tax, levied on top of the county and state taxes. Some counties in WA have no corporate tax.
We're likely going to locate a new manufacturing business in Kalama WA, in Cowlitz County - no corporate, county, or city taxes and the sales tax in WA is 3-4 points less than OR's income tax. We're not big enough to warrant a snort or second thought by the local governments for a tax break.
As to your situation related to the "WA tax" bit - where is the delivery to? A delivery to a locale like Vancouver or Seattle would be subject to state tax, county tax, and city tax - providing proof of residence on top of that. If you buy a widget with a Vancouver WA or Seattle WA "address", you'll owe 3 entities. Some agencies are getting pretty aggressive with tax collection. As I wrote in my OP, I'm on Hayden Island which I-5 bisects, so wrong side of town! - I-205 is on the east side of Portland (near where the Airport is) and I'm in the central area.
If I were you? My two business partners work here in Portland, but they live in Vancouver. The taxes are lower, their wives work in Clark County, but they deal with nasty traffic daily as a sacrifice to their families. FWIW, the Blind Schools in Vancouver are very progressive and absolutely beyond reproach - I've known and collaborated with students and staff there going back to the late-'80s, and the transit authority in Clark County (C-Tran) serves that community well - that School is - and has been for decades - a source of pride of Vancouver. As to the commute through Portland - get a really good traffic app as you'll need it - there's only two bridges between here and there... I'm only on Hayden Island because my brother and I own property here that's already paid for, but we're already looking to sell and relocate.