I firmly believe that the more closely we can get to providing the general conditions in which chickens evolved (feed, habitat, flock size and make-up, etc.), the healthier a flock will be. Allowing a flock to move toward this original lifestyle should be a prime goal for all chicken-keepers.
I look at this from a different perspective. I don't want a flock that is prepared to survive and thrive in a straight wild situation like they evolved in. I want one that can thrive in the situation I provide. I cannot raise a feral flock due to where I live, I have to manage them too much. I think a lot of people on this thread are in the same situation. We are all going to be different, we have different goals and situation. There is a lot of good information in here, obviously, but we each have to take what we need.
I'll fall back on how Dad raised his on his farm in East Tennessee since I think that is closest to my experience to what Lauren was talking about when she started this thread but it is not a perfect match. His flock fed itself almost every day of the year. If there was snow on the ground he'd toss them some corn. Not a lot, but some. This was not as harsh as it may sound. They were part of the life cycle of the farm. We'd get pigs in March and butcher them in October. All kitchen scraps and garden and orchard wastes and excess went to the pigs. But once they were butchered and nature provided less forage for the chickens the wastes went to the chickens. Dad fed hay to the cattle, just spread it on the ground. The cattle could not eat the seeds that fell out of the hay onto the ground, but the chickens could. Like the wild birds that overwintered the chickens could fine a lot of food during the winter anyway, but the food available helped them get through.
Most slept in a hen house, some slept in trees. This was in the country, pastures and woodlands all around. We did not have bears or mountain lions as far as we knew, but we had all of the other predators, four footed and winged. We might on a rare occasion lose a chick to a snake but lost very few adult chickens. Why?
Dad kept his fence rows cleaned out, no easy camouflaged paths for foxes or bobcats to use. Human activity kept them away during the day. Dad was an excellent shot, if a potential predator was spotted it may not live long. If a neighbor's dog killed your chickens they (the neighbors) expected you to shoot it. Can you imagine doing that today where you live? One time a fox started taking a hen every morning. I spotted it one morning doing chores. The next morning Dad was waiting with the .22 and killed it. Predators could do a lot of damage unless they were carefully managed. Hawks were protected way back then but if one was hanging around Dad had other priorities than protecting it.
Breeds. The base flock was probably partially descended from some of the game chickens pioneers brought into the area in the 1700's. Other breeds had been mixed in along the way but they still had a lot of game in them. One time Dad brought home a dozen Dominique chicks, another time a dozen New Hampshire. We raised them in a cardboard box on the back porch and fed them mainly corn meal until they were three weeks old, then turned them loose near the hen house. They were then on their own. Even domesticated breeds from a hatchery had the instincts to survive and thrive. They were raised in a multigenerational flock, sort of, but formed their own sub-flock until they forced their way into the pecking order. There is always the debate between instinctive and learned behavior. In my opinion they can learn some behaviors but I consider instinct to be very important.
He'd keep a rooster and the pullets from them to help genetic diversity and to improve the quality of the flock. Probably about every 6 or 7 years he'd get a new rooster. His overall flock had one rooster and about 25 to 30 hens. The hens went broody often enough that they raised all of the replacements we needed plus we ate chicken every now and then. There are many different ways you can manage genetic diversity. This is the way Dad did it.
Dad was not concerned that every hen had to lay 5 or 6 double extra huge eggs every week. The smaller eggs cooked as well as larger eggs. We ate a lot of eggs, any surplus could be taken to the country store and traded for coffee or flour, stuff we could not grow ourselves. Each cockerel did not have to dress out at 5 pounds at 12 weeks. Mom could feed a family with 5 kids on a small hen. It was more important that the chickens could take care of themselves and provide a lot of eggs and some meat for us so we did not have to spend much time or money supporting them. We did not have much money and we had a lot of other things to spend our time on. Dad did try to improve the productivity of the flock buy bringing in the Dominique and New Hampshire. He did improve it some but after the first generation they were all mixed breed mutts anyway.
I hear that you shouldn't add an egg to the clutch after she begins sitting on them, so it seems like a very time-sensitive undertaking.
The important thing is that all eggs are started at the same time. You can keep a fake egg or two under her (or real marked eggs if you want) until you collect all of the eggs you want her to hatch. Then remove anything under her and start them all at the same time. If it takes you a week or more to collect all of the eggs you want her to hatch it shouldn't matter the vast majority of the time. This stuff really doesn't have to be that hard, people have been doing it for thousands of years. What makes it so hard is that so many of us have lost touch with that background. We left the farm after WWII and moved to the city so we have no experiences to draw on. We don't know how simple it can be. Another part is our expectations. Many people on this forum only want the best. The largest eggs, the most white meat, the prettiest chickens. I don't have to have the best. To me, good enough is good enough. After you get to good enough (I'll quote Bill Murray) "it just doesn't matter". That is my opinion. Others feel differently.
For any that have made it through my long post, my thought is that you do not need to follow what I do, what my Dad did, or what anybody else does. If you have pets, don't treat them like livestock. If you have livestock don't treat them like pets. If you use an incubator you probably do not want a hen that goes broody, too much trouble. If you can't free range, you can't free range. If you can't stand to lose one chicken then take predators very seriously. I find that chickens are very adaptable, but some are better for certain situations than others. It may take trial and error but find what suits you.
And never be afraid to ask a question.