Centrarchid could really give some pointers here. He raised many flocks free range next to each other and goes to great lengths to study their behavior. I’ve had some experience with this but I’m always learning something from him.
It’s pretty much like Canoe said. Each rooster should set up his own territory and defend it from the other. If they are close enough to each other that they come into contact there is a pretty good chance there will be a skirmish while they set their boundaries. There is always a chance one could get seriously injured or killed when they fight but when they are free ranging that seldom happens. Usually one runs away from the other once they figure out which one is boss. If you cannot see your neighbor’s chickens I really don’t think you have any worries at all about this. It’s just not going to happen.
There are different opinions as to why roosters crow. One pretty popular opinion is that they are saying “This is my territory, stay away” to other roosters much like many other animals mark their territory. From a “survival in the wild” viewpoint it’s better for them to avoid possible serious fights than to actively seek each other out for a fight to the death. Bears, wolf packs, big cats, and many other animals use this strategy. I also hear crowing contests between my rooster and others. The roosters do not leave their own flock unprotected while they go searching for a fight. That would not be wise.
How far will chickens roam? Who knows? I’ve had flocks that spent their life within about 300 feet of the coop, others that ranged close to 1000 feet. Some of that is personality of the flock, some of that depends on barriers. I had a flock where three hens would go roaming on their own while the rooster and the rest of the hens stayed around home. Each flock has its own dynamics and that can change with just one chicken. By barrier I’m talking about fences, fence rows, the boundary between a mowed and unmown field, things like that. Some chickens just blast through those but some stop.