A lot of questions, none with clearcut yes-no answers. A lot of maybe's or it depends.
Does anyone fully free range, no fencing at all?
What you are talking about is a model that has been used on farms for thousands of years. The chickens basically take are of themselves. They are livestock, not pets. To me the biggest issues are predators. Locking them in a secure coop at night can help tremendously, but practically any predator will hunt during the day as well as at night. Typically human activity causes them to be more cautious during the day but several people in this forum have had chickens taken by a hawk or fox within a few feet from where they are standing.
I grew up on one of those farms. Over the years we had two serious predator attacks, a fox and a dog. Both were shot. We had plenty of hawks around, they weren't a problem. Some people lose a lot of chickens to hawks or eagles. A snake might occasionally take a really young chicken a broody hen was raising but even that was really rare. Did not happen most years. Others that try free ranging are wiped out immediately.
How successful from a predator standpoint will you be? I don't have a clue. I'd think your biggest threats during the day would be coyotes, fox, dogs, hawks, eagles, and maybe a bobcat. A trained Livestock Guard Dog that stays with them can help a lot with some of them, but only if they stay with them.
Will they lay in the coop when they are put up for the night or am I going to end up searching 69 acres for eggs?
Most of our hens laid in the hen house. Most does not mean all. We'd have a few that hid a nest somewhere else. Typically two or three out of about 25 hens. Most of those were in a hay barn but they could be anywhere. As the oldest boy my job was to find those nests. I did most of them but certainly not all. Occasionally a hen would show up with a bunch of chicks, I often could still not find where they had kept their nests.
We have a bunch of different kinds of breeds. About how much food would I feed per bird?
How good is your forage? In Tennessee our chickens pretty much fed themselves year around. In winter we'd supplement that some with corn we grew ourselves, but not a lot. More when snow was on the ground. We also had horses and cows. Some chickens would scratch through where we fed hay, looking for grains. They also scratched through the cow or horse poop, looking for partially digested bits. Not all even did that. In our climate they found a lot to eat, even in winter. I anticipate your area to be pretty dry, your forge may bit be that good. I don't know how much you will need to supplement them. Probably not much in summer, more in winter.
Also on free range would they still need the grits and oyster shells?
What is your native rock? If it is limestone they will probably get all the calcium they need for egg shells from eating that. Your egg shells will tell you if they are getting enough calcium or not. If they are firm and hard they are getting enough calcium from somewhere. It never hurts to offer oyster shells. if they need it they should eat it. If they don't need it that oyster shell you offer may last a long long time.
If your soil has rocks in it, they will find their own grit.
Many people on here try free ranging. Some find out quickly it is not for them, others do OK. I wish you luck.