Bare backs can be from the rooster, but bare buts, chest and bare around the big tale feathers suggest feather picking. It may be caused from crowded conditions (which is not your case), or something missing in the diet. 18% should be good, but if they are doing it, something is missing.
I had...
Start giving them Black Sunflower Seeds. Also during first few weeks you can give them a can of dog food once a week. More often in the beginning and seldom after few weeks.
Make sure the feed (pallets) you are giving to them is at least 16% protein.
If you notice hen who is overly aggressive...
It is Australorp - clean legs, pink skin. Both breeds have similar feather genes, so as babies they look the same sometimes. When groan up BCM should develop more red feathers.