As it sounds like you are aware, some breeds are more prone to brooding than others. Put another way, some breeds have had the broodiness largely bred out of them and others have not.
When I first started this venture, I thought it would be cool to have broody hens raise batches of chicks. After doing my research, I got some Buff Orpingtons, since most people seemed to agree they are very prone to broodiness. I even got them from a breeder vs a hatchery, to ensure an even greater chance. Then I sat back and waited...and waited...and those hens got older and older and never did show even a day's interest in brooding.
Meanwhile I had a variety of other hens for egg laying and wouldn't you know, it was a BSL who finally went broody on me. And when she was a year and a half old too! So sometimes you can't plan for it.
I've heard Cochins and Silkies are your absolutely best bet for broody hens and good mothers. I've yet to have either of those breeds but others will probably vouch for them.
As for where to keep them, if they are broody and raising chicks it is a good idea to segregate them from the flock. However I wouldn't go overboard on separating them until that time comes, since you could get broody breeds and still never have a broody hen.