I have 10 nine week olds and 23 five week olds right now. I kept them in the house for 3-4 weeks and then moved them out to the insulated coop with heat lamps. The 9 week olds are doing great, well feathered and mostly assimilated into the adult flock (which is just 3 hens and 1 roo). They had time to acclimatize to the falling temperatures this fall and have had access to the covered run since they were 5 weeks old.
If I'd been smart I'd have stopped there but I hatched a second batch. The littlest ones (5 weeks) are more of a problem because it's now too cold for them to go out into the run. Plus the coop is raised with a ramp, and it takes time (days, weeks) for the little tykes to figure out how to get back up into the coop. Not a problem when temperatures are reasonable, but a big problem when it's too cold out.
So I've got my coop divided into two sections for the different ages of chicks, and the adult birds are sleeping in the feed room. It's kind of complicated and I spend a lot of time making sure all their needs are being met. If it were spring instead of winter all this would be much simpler! And then there's the cost of running those heat lamps 24/7...