This novice is looking to buy an incubator. Only have 4 hens I want to breed, right now. I anticipate breeding them is as much fun as having them so my flock will grow. What features should I invest in, for now and the future. eg. moving air, humidity control, turner? If temp and humidity is so important can I open the incubator to turn the eggs manually? Can I add more fertile eggs to the ones already in the incubator? When eggs hatch do the chicks change the atmosphere in the incubator? How soon do the chicks have to be removed? Thanks for any advice.