I understand, it is a staple food for almost all animal based feeds. So with that said, feeding them corn won't hurt anything because like you stated it has been done for a long time. And I am for one not one to judge. The chickens will tell you if they like it or not. Their the only ones...
Now for what I know of corn, it has no nutritional value except as a sugar. So I'm not sure if I would personally. We give ours worms and bsf as treats as well as any kitchen scraps that don't make it to the compost pile. Just my 2cents.
Free range has worked for us in chicken tractors. However, it's does require some room. Now we have moved and don't have that kind of room. So we're stuck with feed I am working on a personal feed. I'll post again when it's more concrete.
We have a standard of a week. After that a quick candle and if any question it's out. We have tried the pinhole but we have never had any good luck so we just kept it simple. You masters that can pinhole are amazing by the way. Lol:D