It appears that you are really attempting to do your homework MarcRuval. I viewed your North Washington average weather chart. As weather conditions go, it really doesn't seem that extreme. Generally the weather appears very very good. Excellent for grass/hay growth.
One thing that you haven't mentioned at all is help. The size project you are envisioning requires an extensive commitment of funds. You have very good intentions and seem to have a very large capability to learn about animal husbandry. Farming and ranching can be hard & timely work. The amount of money you can lose and the amount of resources one can waste can be directly proportionate to the capital invested.
If you were to purchase as many cattle as you are discussing, I recommend that you ensure that you purchase quality healthy cattle. That requires a working knowledge of EPDs and an ability to evaluate potential breeding combinations and the ability to select useable cattle based on sometimes minimal physical viewing opportunities. That is just to start. After you get started into your first year, you need to consider improving successful breeding rates (probably synchronizing breeding) reducing calf mortality rates, proper nutrition, maintaining & operating equipment, and eventual marketing strategies (private treaty, stock auction barn, production sales, etc..).
You would need an honest, competent ranch manager for I would estimate a very very minimum two years (and probably 4). You can lose your tail with out some dependable help. I estimate that help would cost you 30 to 40 K annually.
I think your biggest concern in providing shelter would be to young calves. That is another reason to synchronize and split your calving into two periods (Spring and fall). Avoid the potential for extreme weather conditions and therefore, hopefully minimize your calf mortality rate.
I think you could use a partially covered livestock handling area for your squeeze chute. Pole barns and metal buildings should be available locally. Check your local rural electric cooperative magazine for some sources of builders.