I tend to agree with leaving him with the girls as long as none are being injured. If the girls are being injured, such as a cut, that is bad and you need to do something. The two areas to watch are the back where his claws are grabbing during mating and the back of her head. Part of the mating act is that he has to grab the back of her head, that's her signal to raise her tail out of the way so he can hit the target. If you see cuts or blood there or on her back it is time to do something.
Some flocks of hens really like having a rooster around. Others seem to be a lot less stressed if you remove a rooster. Each chicken has its own individual personality and each flock has its own dynamics. That's a big part of why I like to make my decisions based on what I see instead of what some stranger like me says over the internet.
You certainly can. They are yours and you can do what you want. There is a danger from predators but lots of people free range without problems. Others are wiped out almost immediately. I'd lock him up securely at night, that can help a lot against predators.
You don't get guarantees with chickens and behaviors. I'd expect him to hang across the fence from the girls for a lot of the day, though foraging some. The girls will likely hang near the fence across from him a good part of the time. Would they prefer to be together? Probably, especially him. But they should be OK apart like that.
I don't know where you are located. Since they are 8 months old that kind of implies you may be south of the equator where seasons are switched from here so molting would be swapped. If the entire feather is out the feather should grow back reasonably soon. If any part of the feather shaft is left then the feather will not grow back until the hen molts.
