My thoughts and opinions, get a bigger coop. Somehow I think you will need it later if not sooner. I think you have started down a slippery slope. :oops:
I'd give myself access to the littles' run space. I'd be willing to bet you'll need to get in there. Hopefully that is in your plans...
I like having my brooder in the coop. The chicks essentially grow up with the flock, which I think makes integration easier. And they are trained to return to the coop at night. For this to work you need electricity to the coop and you need a coop big enough. The hardest part of this to me...