We sometimes use a 60-100w bulb on a timer for extra light. A draft free coop is a must, with proper ventilation. Just enough heat to keep things at 34-35°F is all you need. We keep a heat lamp trained on the waterer, and it keeps the water from freezing and keeps the coop just above freezing. Let the chickens adjust to the cooling temps, and they'll do fine. The deep litter method really does keep them a little warmer... the composting in addition to insulating from the cold ground helps. 2x4's with the wide side up so they can sit on their feet to prevent frostbite, and if you have single-comb birds, a little vaseline rubbed onto their combs will help keep them free of frostbite. Throw out a little bit of corn just before bed, and keep an area of their run free from snow and you should be good to go.