First question I think that would be good to know is: how far would your pigeons need to fly to find corn/other grain that they would eat? And if they are eating out of neighbors fields/hanging around your neighbors silos are they likely to get shot there by someone else?
I think the idea of having free ranging pigeons that forage on their own is doable, it used to be done in earlier times, that’s where the big dovecotes in Europe came from. People wanted the same things in a meat source you’re looking for.
I wouldn’t recommend feeding bread, I know some freaks in cities will eat it, but it’s not really great for them and doesn’t really sit well with their digestive systems. Peanuts, on the other hand, some pigeons love. I used to feed my racing pigeons peanuts as a treat sometimes. It can take some getting used to for the pigeons because peanuts are so big, it can be hard to get into their beak and oriented so they can swallow them. Feral pigeons are a bit small than homing pigeons, so I could see them having a harder time eating peanuts, but it may work. I’ve had pigeons eat whole kernels of field corn, so if some people’s birds don’t eat it I think that’s just a matter of them not being hungry enough/picking what they like best.
The key to your system is getting the pigeons to come back, so that means making their home appealing in some way so that they want to return. That could mean having a nice place for them to roost, their mate being there, or food or water. If you started off with mated pairs, leaving one bird from a pair out at a time would likely be a bigger draw for the other to come back. That mate at home being on eggs or young would also increase the odds of its free ranging mate returning.
When I raised and raced homers I fed about an ounce of feed per bird, per day. I would not ever just leave feed out for them to eat whenever, it’s a good way for them to waste it. If I were you I think I’d feed in the evening (maybe starting out with half an ounce per bird) before it gets dark, because the birds should already be coming back to roost. Then they could leave in the morning, do their own foraging and come back the next evening to get some food again. I would probably start developing this routine of feeding at night with all birds locked in so they get used to it, then start decreasing the amount of food they get and releasing hem throughout the day.
I know everyone says pigeons mate for life and it’s a nice image, but they don’t. I have broken up many pairs and got them to mate with other birds, as well as having some already mated birds take on a second mate. The key to relating birds is essentially locking them together in a cage, it helps to start this at night so they hear each other all night and by the morning are somewhat used to being close to the other pigeon. Based on your initial plans, I wouldn’t cross in any utility breed pigeons, it could possibly make the offspring bigger, but will likely negatively impact their foraging ability, homing, and possibly flying ability (some utilities get pretty heavy and don’t really fly much if at all).
I guess one question I have is are you planning on eating the adult pigeons or the squabs? I think when dovecotes were popular most people kept them to have a constant supply of squab. If you’re used to eating pigeons that have flown a lot and don’t find them tough, great, but I think that’s why the tendency has always been for most people to eat only young pigeons.
For predators, hawks can be a pain. One thing I used to use was crow decoys, which I would move around every few days. Most hawks don’t like crows because crows tend to chase/harass the hawks.