I'm not opposed to free-ranging -- I hatched my original peas from abandoned feral eggs, from a free-ranged flock that went feral. But for the last 5 years, I've been reading tale of woe after tale of woe, first over on the now-defunct UPA forum, and now here on BYC, from people who thought free-ranging would be just the thing. They are shocked that their birds didn't come right back. They are horrified that their dogs have eaten their peas. They have no idea how the fox/raccoon/coyote/snake/hawk found and ate their hen's eggs (or ate their hens) while the hen was hiding her nest in the forest/field/bushes/backyard. They cannot comprehend why their peas would choose to roost in the trees rather than the cozy coop. They are astonished that peas will wander in search of mates (or in search of more mates) and can't believe that peas calling for mates can be heard a mile or more away. They are heart-broken when their beloved chicks never return, or are consumed by a predator, as if real life were really like an actual episode of a nature documentary. They can't figure out how to worm or treat the peas they can't catch, and then they grieve when their birds succumb to gape worm or respiratory illnesses. They learn, the hard way, that peas get hit by cars. Or get shot (or poisoned) by disgruntled neighbors, who are irritated by the peas stomping on their rooftops and ravaging their gardens. They turn the birds loose and can simply not understand why everything did not work out exactly as planned.
You asked if your free range plan was a good idea. In return, I asked if you have thought through the various possible adverse outcomes, and whether you are willing to accept those risks and probable losses. I don't know what "perfect for free-ranging" means, or where you live, or what kind of predators live in your neighborhood. I just know hens become dinner for the food chain during breeding season and a lot of free range birds don't survive. Others do, they thrive and even successfully reproduce. Successfully free-ranged peas are wonderful. But there's no guarantees on survival.
About that herding thing -- sometimes it works, sometimes it doesn't. Peas are really good flyers...
Good luck!