OK, I see I'm late to the party, and don't have the experience of most of the other posters, only benefit of a lot of reading, and some odd quirks in the way my memory works. (its a disorganized mess in here!)
So, in no particular order.
You have 32sq ft. less structure, less roost boxes, food, water, and anything else you put in there. Its big enough for not more than 8 (bantam) birds, likely closer to 4 or 6 full size, depending on how much room your nest boxes take. Brahma start small, grow slowly, but they become big birds. I'd call that space for 5 +/-1
On that subject, you have too many boxes. Two will meet your needs, easily - and you will benefit by making them outside accessible through a hinged door or similar. You want a small lip on the nesting boxes to help keep bedding material in, and you want them raised enough that soiled bedding doesn't start making its way into the egg laying area. Say, 6-8" off the floor, with 1x3 framing for the lip, either 3/8" or 1/2" osb structure. A few pieces of peel and stick tile will aid the occasional nest cleaning need, as will a cheap piece of vinyl flooring on the main floor - or several thick coats of good paint.
Your roosting bars you want above that, to encourage birds to roost not in the nesting boxes. While the heights you propose for your roost bars are not unreasonable, remember that keeping drafts and moist air - particularly in the cooler months - off your birds is a priority, and the bird itself takes up space above the bar, which moves the lower height of your windows up. You get some credit here because while Spokane is cold, its also relatively arid, with roughly half the US annual precipitation rate, and most of that in the form of snowfall. I'd drop roost height to 12-15", and put both bars at the same height. Truly, you only need one, given the flock size. They are so low, poop boards probably aren't practical - something to keep in mind as you consider your litter method.
The "rule of thumb" is 1sq ft of ventilation per bird. Assuming 4 birds in your house, that's 4 sq ft of ventilation, or 576 sq inches, minimum. Each 2" dia hole you drill offers 3.1" sq inch of ventilation. You need about 200 of them. Sorry, that looks worse in print than I intend.
The point is, even before reducing their effective ventilation area for the louvered coverings I imagine you will use, they just don't offer enough air flow to be worth the effort. Even using 4" soffit vents offers just 12 sq inch per hole. The little 2" vents are to allow trapped moisture to escape structures that might otherwise accumulate between a facade (often brick or stone) and the stick built structure behind it, while the round soffit vents were popular retro fixes when adding ridge vents to equalize airflow.
The other windows you've proposed, two at 9x9 are 81 sq in each, or 160 sq inch total, and three at 8x14, 112 sq in ea, 336 for them all. All told, you have less than 500 square inches of ventilation - almost enough for three birds, not four or six. Since you are rapidly running out of wall space, I'd normally suggest soffit venting on your overhang, but you have no soffits. Where else, close to the roof line, can you locate venting without impeding on structural elements?
Lighting is up to you, I recommend LEDs, minimizes fire risk. You don't need heat, particularly with the Brahma, unless you are brooding chicks - which you won't be doing in that hen house for a host of reasons too lengthy to list here.
Raising it up on 2' legs is a great idea, for a host of reasons, but your structure will be too heavy for wheels unless you intend to put riding lawnmower tires on it, and run it on a 5/8" bolt driven through the leg. Even then, you will need to tow it, carefully, as it will be top heavy. Tow bar on the WIDE side for stability. Assuming you scrap the wheels idea, you do want to secure it to the ground somehow for the occasional high wind, and orient it so the narrow side faces your prevailing wind direction. Whether you do that with sunken legs and poured concrete, buried cinder block and chain, earth augurs and steel cable (shed tie down kit) or some other method depends mostly on local soil conditions. I can't research those for you from here.
You get snow, about 4' per year, and your roof pitch is roughly 3/12. It won't shed itself, but that's a small area to clear off periodically, even if not at a convenient height. What are you doing for roofing material??? and how did you frame your rafters for snow load?
Finally, what are you doing for your run, which can help compensate for a number of shortfalls in optimum coop? Or are you fortunate enough to be able to allow them to free range in all bust the worst of weather?
Oh, and on light, heat, and frozen water supplies for your birds during January, where your average high is 33, and average low of 22, how are you running power and water to the structure, and keeping that water from freezing??? Your fire risk (assuming you use LEDs and skip the heat lamp) is more likely in an extension cord and power strip then any other place in this build.
That's what I've got, from a place of wanting to help, not any desire to tear down your efforts. Apologies I've not the words to frame it better.
/edit and I have Dark Brahma. Love the coloration on your Lights, they weren't available to me or I'd have gone that route, instead of dark. The choice of Brahma at all in my climate was with *some* trepidation, they are much better suited to yours. All the best to you and your family on your build and your flock.