Plan on allowing at least 8 inches of roost for every hen that you raise. Chickens tend to snuggle during the cold months to keep their bodies warm. You can go beyond the minimum of 8 inches. A roost must be higher than a nesting box because chickens often seek higher ground for sleeping. You also don’t want them to poop on the nesting box.
As for the nesting boxes, chickens want to share them so provide at least a single box for every 4 hens. You can put herbs inside the nesting box and curtains but they’re optional. However, your chickens will adore you if you do. Pine shavings as well as straw make great bedding options for nesting boxes.