The way I read your post you plan to keep the current nine hens separate forever and get some new chickens (I assume pullets) later for the new area? I don’t know how old these new pullets will be when you get them. But then you mention putting the cockerel with your current flock. I’ll admit I’m just a tad confused, especially about the three young comets. My guess is that you plan to keep the cockerel with the three comets plus whatever new chickens you get. Are you south of the equator so the fall molt is coming when you will butcher those six older hens? I’m trying to work out timing and sequence of how this would go together. If you modify your profile to show a general location that can often help with questions. When you are talking about integration the age of the chickens involved can be really important. You’ve given age except for the new additions and when you will get them.
What predators were taking your chickens? Were they flying predators or land based? If it is installed and maintained properly the electric netting should stop any land based predator. The netting does not work well in snow. Grass and weeds growing up in it will short it out. Dried leaves or other debris can pile up against it in a heavy rain or wind. When those are wet they short it out. They don’t shock anything if you have a power outage. Chicks less than 7 or 8 weeks old can walk through the netting without getting shocked. With all that said electric netting is still very good. Once a critter is shocked it tends to give that netting a wide berth whether it is hot or not. The problem with that is that new predators are being born and weaned on a regular basis and that people can abandon dogs at any time. Still, I’ve had electric netting about 6 or 7 years and never lost one to a land based predator with snows and power outages. Before I got the netting I lost some with a mature rooster in the flock. In those incidences the mature rooster survived but members of his flock did not.
I lost three to flying predators, an owl at night when I was late locking them up and two to hawks. There was a mature rooster with the flock in all three incidents. To me a mature rooster is very marginal as far as added protection. The main benefit is as a look-out but often the dominant hen will take over that role if there is no mature rooster in the flock. I have seen a rooster chase crows out of that netting area when I tossed some fresh protein in there for the chickens. I like the way Chullicken phrased it, there are tales of bravo out there that happen, but my roosters were cowering in the coop while a hawk was feasting on a hen.
Another benefit to a good rooster (not all are good) is that if something is suspicious he will get between the flock and it and check it out. I think that’s where a lot of the stories of a rooster sacrificing himself comes from, him checking out a threat. With mine they tend to lead the flock to safety if a threat is established, not keep himself between the threat and the flock. With the electric netting that won’t be necessary because ground based predators should not be a problem. With flying predators an alarm is sounded and they run for cover if they see it in time. As I said it is marginal how much protection you really get from a rooster. To me the only reason you need a rooster is if you want fertile eggs. Anything else is just personal preference.
When chickens mate the hen squats. Basically she lays on the ground. That gets the weight of the rooster into the ground through her body, not just her legs. That’s the way nature protects the hen during mating. Most full sized breed roosters are usually 2 to 3 pounds heavier than hens of the same breed. You are dealing with living animals so of course things can happen, especially if the hen does not do her part. Some people keep bantam hens with full sized roosters without issues, but the more weight difference the more likely you are to have issues. Personally I would not hesitate to keep a Jersey Giant with the hens you mentioned if he fit my goals. But as you can see others have a different opinion.
Back to your original question. “so I'm not sure if having to establish pecking order/dominance so close together would be problematic.” I don’t think it will be any more problematic than spacing it out more. It’s the actual integration I have questions about, no matter how it is spaced. By the time quarantine is over he will be 7-1/2 months old. Mature hens can be pretty brutal to an immature cockerel but cockerels mature at different ages. Different hens have different personalities too. People tend to forget that the hens have a part to play in this too. I’ve had cockerels about five months old be accepted by a flock of mature hens. I’ve had one eleven months old still have issues with the dominant hen. Jersey Giants tend to mature later than many other breeds but they are still individuals. It’s quite possible if you add him to a flock of mature hens there will be a lot of drama down there or it may go extremely smoothly. I just don’t know.
Then there is the question of how old the new ones will be and the make-up of the adults when you integrate them. If it is a mature rooster and a bunch of young chicks I don’t see a lot of advantages. If those three comets are thrown into the mix it changes some. I like raising chicks with a mature flock. The young ones tend to form a separate sub-flock until they mature but I think they learn a lot from being around the adults. I think it helps strengthen their immune system too but you can accomplish that by tossing some dirt from the adults’ run to the chicks. You’ve been through an integration before, you know how to integrate pullets with hens. It’s not that different if a mature rooster is in the flock.
I don’t know what your ultimate goals are. Personally I discount the benefit of having a rooster in that electric netting area, though others will disagree. With my goals I’d not get that Jersey Giant but get a bunch of mixed run chicks or pullets with one cockerel. Eat all but one cockerel. Since you plan to butcher those hens you can butcher. When they are going through puberty and you are waiting for them to get to butcher size it will probably get really dramatic down there but many of us go through that on a regular basis. My set-up is pretty similar to yours with the electric netting and a second coop. Lots of space really helps. Most years I don’t have any issues with the cockerels that the chickens can’t handle themselves but occasionally I separate some or all cockerels in that second coop/run until they hit butcher size. Each chicken has an individual personality and each flock has its own dynamics which can be changed with the addition or subtraction of one chicken if it is a dominant chicken, male or female.
What you are talking about could work if you decide you need or just want a rooster. It would reduce the potential drama of raising a cockerel with the flock from a chick. But you may have a lot of drama when you introduce him at 7-1/2 months to your established flock. There are risks both ways.
That’s enough this morning. Hopefully you will get something from this that helps you make up your mind. I have to take the computer to the shop soon so I’ll probably be offline for a few days. I’ll check back when I get it back. Good luck, I think both ways could work.