I like that idea of the slanted roosting deck.
Rita, we have about 30 right now. I plan to soon order another batch of chicks.
As for a separate brooder house: we have the closet in the coop with power and I think that we'll use that closet for raising new chicks. It's 4x12 in size which is plenty enough for a water trough and a heating lamp.
Our old coop is 8x8 in size and I think we'll convert it to a meat bird coop where we use it only a few times a year to raise a crop of heavies. That, or we'll turn it into a garden shed. Haven't decided that yet.