There is no Nitrogen/dust connection. Two seperate entities. I had nitrogen in my tires but it seems that at least in my tires its no more stable than air. My low tire light came on after the temp dropped significantly several weeks ago. I thought I'd made it when the light didn't come on back in the fall when the temps dropped. I filled them with plain old air since I am switching tires in a few weeks. All four had dropped several pounds.
As for the brake dust the rotex are the way to go but I'd also invest in a 12-13" rat tail brush so you can get in behind your spokes when you clean your wheels. Makes a world of difference both in keeping the dust off your wheels and the appearance of the wheel.
Pat