This is my first winter with chickens and I, too, was worried about providing heat for my hens. A trusted friend told me simply, "if you baby your hens, they will die." I followed his advice and heat only their waterer, and was very amused to find that my largest hens are choosing to roost ON...
For the past 3 months I've had 1 duck living with 6 chickens. The only time there's any conflict is at mealtime and one of the hens sometimes pecks him, but then she pecks the other chickens too. Nothing serious. I let them free range when I'm home and the duck is the leader of the flock...