Absolutely....even better if it's out of sight of the flock, especially if you leave one cock/erel in with the pullets.
If you're getting more hens you'll have to integrate them into the existing flock, best to have a separate but adjacent enclosure for that too.
There are many ways to...
Only time will tell.
Once your cockerels reach sexual maturity at about 3-4 months, they may fight and both will try to mount the pullets... before the pullets are ready.
Males reach sexual maturity before females do....it ain't pretty and can be quiet alarming if you've never seen it before...