Light won't affect your girls since they are that young. Usually light only applies to chickens in their second year. IE: Chickens hatched spring 2011 will slow this year without 14-16 hours of light.
I don't add extra light. I like them to save their energy for keeping warm. Plus it helps keep them laying for a longer period of time. I am attached to some of my birds, and want them around and being productive for many seasons.
If I told you how many birds I have, and how many eggs I'm getting it would seem absurd. I have a lot of young chickens, so they shouldn't count in the # - but the total adult birds that have laid, and could lay on a daily basis is a number I haven't calculated yet. I have over 150 chickens, and get 5 eggs a day on one end and 7 in the other pen. 12 eggs a day is my best right now lol.