I totally know what you mean about the dust! My first batch of chicks stayed in the house for about 4-5 weeks before I just couldn't stand it anymore. I was using a heat lamp back then and was always stressed about how they could survive outside... so much worry for no real reason at all. Chicks are much more resilient than we give them credit for sometimes!
And yes, a coop brooder is a lifesaver!!
Those all sound like good ideas to me and your coop looks awesome! But if you're planning on building a brooder under the roosts (which is a perfect spot!) why not just make the "roof" part permanent? The front can still be removable like you say, but that area may come in handy at any time in the future if you need to separate an injured bird that needs protection, or if you want to separate a mean bully.
You can also turn that roof into a poop board or tray, which will make clean up sooooo easy. I fill mine with Sweet PDZ stall refresher and just scoop it like cat litter into a bucket and toss it in my compost bin. The rest of the coop is pine shavings. Since most poop in the coop comes from roost droppings at nighttime, the shavings only need to be cleaned out once or twice a year. The PDZ is also excellent at keeping away odor and ammonia fumes. A poop tray/convertible brooder is a win win!