I've done free range chickens, let me know if you have any questions.
When talking about supplementing their feed, how many eggs you are getting and their size should be the best indicator of if they are getting enough nutrition.
The best thing about free range chickens (aside from the flavorful eggs) is that the more "range" they have the greater their ability to forage for bugs and feed themselves. They will be getting pletty of calcium from eating bugs if they are getting the chance: that with your kitchen scraps might be an adequate diet, but if they need more calories, cracked corn is the most typical dietary supplement. It looks like someone else already commented on the egg shell thickness and calcium.
The really only need for fencing is to deter predators, so you would be the one most aware of what your local predator situation is like. We had plenty of hawks where I kept my birds but because they were 100% free range, if hawks flew over my guinea fowl would raise the alarm and all the birds would run for cover under trees where they were safe. My free range birds were actually so big and tough from foraging all day for as much food as they want, that two of them got grabbed at by hawks when they were too slow for cover, and managed to get away, so I never lost a chicken to predators out of the about 30 that I kept. (guinea fowl, different story lost plenty of those)