Here is what I can deduce so far: First off, you have 2.5 weeks so don't waste your resources now, stockpile them as much as possible. I can't see any reason to take a Storehouse if you aren't a gatherer, since they don't speed up your work orders, it just lets you have more of them so you don't have to check them as often. Turns out it is more of a "lazy" building than I first anticipated in my reading on it. I find it almost worthless.
As for the Salvage Yard, you WILL want it as a raider, but since you can't get it til later regardless, build your profession buildings first, start your mine and herb garden, and get some work orders going.
And last, it sounds boring and you won't keep it forever, but for the first few weeks at least, I'd get the Lumber Mill and harvest trees. You are GOING to want a vast supply of Garrison Resources, and upgrading is not cheap. The extra flow it provides is going to be invaluable to you for the first 2-4 weeks. At a certain point it will become superfluous and be replaced by another building, but right now I feel it is absolutely essential to getting things to max level.