That's a lot of chickens.
I've never brooded more than 50 chickens at a time. I've only raised smaller numbers of chickens in a tractor, as a grow-out pen. When they were large enough, they started free ranging.
For larger numbers of chickens, I've always used stationary housing. They've usually free ranged over 3-4 acres, with the housing fairly close to the middle of the acreage. The acreage has been sectioned off into multiple pastures or foraging areas. If there's good forage available, mine are enthusiastic about getting out there to eat it, even though I free feed their layer food. These days, I also have water available away from the coop in warm weather, so they don't have to go all the way back to the coop to drink, if they don't want to.
They've covered as much as 5-6 acres when pastured with sheep. They would follow the sheep as the sheep moved to various grazing and browsing areas. The sheep had a stationary housing, feed and water area. In the morning, the sheep would move out through whatever gates we had open, depending on where we wanted them to go. At night the sheep would come back home. I opened a chicken sized gate to let the chickens into the sheep area in the morning. The chickens liked hanging out with them and seemed to feel safer, as they were bolder about exploring new areas. Wide open spaces put chickens at risk of attack and that's something they tend to be cautious about in a new area. The chickens would come back to lay eggs in the coop as needed and then go out to forage again.
My chickens like to forage when there is forage available. If all a commercial operation is offering is dirt, then they don't have a lot of motivation to leave the feeders. What's the point? Foraging is also a learned skill. Young chickens aren't as good at it as older chickens that have had time to learn. They have to learn what is safe to eat, what is good to eat and where it's safe to wander.
Flock raised chickens are taught quickly, while artificially raised chicks need to learn by trial and error or by watching a bolder peer, what to eat and where to go. I walk young chickens to new areas, to help them learn to forage there. They're also happy to follow other animals that they trust, like livestock they know or some of my pets. If they're mainly going to just eat some grass, legume leaves and a few bugs, that doesn't take a rocket scientist to figure out. For acreage that has more extensive plantings, along with fruits, herbs, etc., that can take a little longer to figure out.
Although there may be plantings close to the housing they can eat, they'll go much farther out to work areas for insects.
Having the chickens hanging around sheep in the pasture kept them from being attacked by hawks in our experience. Although I had one dog in particular that was very good at guarding against hawk attacks, not all dogs are as good at preventing aerial attacks as they are at preventing ground attacks. I think it just depends on the dog.
I think the biggest issue you'll have is degradation of the pasture right around the housing. That's an issue just from them going in and out of the housing, even if they're foraging farther away from the housing. On their own, it usually takes them a little time to get enough confidence to range farther away from the housing, especially in a pasture with no cover for them.
There are a lot of variables on how often you need to move housing. You may find that even if you get a lot of information ahead of time, in the end, you just need to monitor the pastures and see what kind of condition they're in.