Sounds like you have a good plan. I'm sorry to hear about the hen eating the egg. I don't know of any way to break an egg eating hen. I think all you can do is cull them from the flock before they start influencing the other hens to do it. I would make sure that the interiors of your nesting boxes are very dark (chickens don't peck what they can't see), and I would put a fake ceramic or wooden egg in each nesting box. Not only will it encourage the hens to lay in the nesting boxes, but it they peck the fake egg, it's hardness will discourage them from pecking other eggs.