Two possible modifications, given that it is inside the garage, and already partly framed:Until this actual moment reading your thoughts, I honestly hadn't thought of it. I think we just got caught up on the coop hype.
At this point, it's pretty much framed and partially built, so we may continue on. I mostly wanted to ensure the chickens were as secure as possible.
You could cover the frame with hardware cloth (contain chickens, protect from predators), and not bother with solid walls. This will be fine for the chickens, will make their space feel more open, and will let you see the chickens anytime you are in the garage. The garage will get VERY dusty, but probably not much worse than your plan of partly-solid walls vented into the garage.
Or you could make all walls inside the garage be completely solid, and add ventilation from the coop directly to outdoors. This would keep most of the dust out of the garage, but makes the chicken space feel smaller, and you can't see them when you are in the garage (until you open their coop & walk in.)