I've been researching diets for chickens and I'm so overwhelmed! Do they need pellets or crumbles AND corn? What about "scratch", and what IS scratch exactly? Do you feed them ad lib, as much as they want? Or will they overeat, so you have to give them set portions? Do they have to be weaned from one food to another gradually, can chickens get upset stomachs like other animals if switched food abruptly? Can you just give them human food leftovers whenever, is it good for them? What about calcium or giving them eggshells or something? Do I buy that in a store or how does that work? Help! LOL!