When I open that link it takes me to a bunch of different coops, not sure which is the one you are talking about. That doesn’t really matter though, if they tell you it will hold 6, they don’t mean like we generally raise them. We don’t generally keep them in commercial conditions, cutting off their top beak so they won’t eat each other, manage the poop the way they do, control feed and lights as tightly as the commercial operations, and other general commercial management techniques.
I’m not a believer in that 4 and 10 either. If all your chickens are the same age, already integrated, and no more than one rooster most people can get by with less, in many other conditions more room is really nice to have. There are just too many variables in our flocks, climates, management techniques, and so many other things that no number of square feet guarantees problems and no number of square feet guarantees paradise. I find the more I crowd them the more behavioral problems I have to deal with, the harder I have to work, and the less flexibility I have to deal with things when they happen.
Chickens do not understand coop space versus run space. They only understand space. If they are locked in the coop section only, then it is coop. If the pop door is open where the run is available it is coop plus run. There can be a big difference. The 4 and 10 isn’t a bad starting place for a small backyard flock, but when you start integrating it really helps to have more. But you don’t so let’s try to deal with it.
I never want to force chickens to be close together, I don’t care if it is during integration or with an established flock. Allowing them to get close together when they both want to is great but it’s very important to allow them to not be close together when they don’t want to be. The pullets are going on top of the coop to avoid the adults. They are sleeping in that crate to stay away from the adults. That’s the way they should be behaving. If you are concerned about the rain, use a tarp or something to help keep them dry, but don’t force them into that coop with the adults. Chickens have been living in flocks and integrating new chickens as long as there have been chickens. Allow them as much freedom as you can so they can use their instincts to do that as safely as they can. Normally when they start to lay they will be mature enough to force their way into the pecking order and they will merge into one flock. Until then the pullets will avoid the adults as much as possible.
Your run size isn’t all that bad though I very much believe more is better. I assume the coop space in that kit is pretty small. I don’t know how predator roof you consider your 12x12 run or that coop and run kit. Those kits usually come with more nest space than you need, that should have at least two nests, which will be good for 6 or 7 hens. Once things settle down and the pullets become fully integrated you might be able to get by if you treat that coop/run kit as a coop. Basically never lock them in that coop section by itself but always give them access to the bit of run that came with the kit. If you consider the kit the coop, that should give them more than 4 square feet per chicken.
I don’t know your climate, wintertime may prove a challenge if you get snow. Chickens often don’t like snow and refuse to come out of the coop the first few days they see it. Mine eventually get used to it and go out, but it takes a few days. If snow is an issue you might want to wrap an area this winter to keep an area snow-free in the run.
In the meantime, set up different feed and water stations so the younger ones can eat and drink without challenging the adults. And those hideouts like Bobbi mentioned. As far as I am concerned you don’t have the ideal conditions with that tiny coop section, but you can probably make it work, especially if you can get though integration. That 12 x 12 run can help.
Azygous that’s the first time I’ve seen that claim about mice not eating fermented feed. I always figured mice would eat practically anything.
Yes, rodents will be attracted by two things. Mainly it’s the feed. Even if you lock the feeders up at night, the chickens normally spill enough in the bedding to attract mice. I’ve seen mice feeding in the middle or the day too, though they are certainly more active at night. A lot more active. Most of the ones I trap are at night. Don’t store feed in the sacks but use a mouse proof storage. I use a metal garbage can with fitting lid.
Chickens will eat mice. Mine generally don’t chase a mouse when they see it, the mice are so quick the chickens don’t have much chance of catching them. But when I trap a mouse I toss it to the chickens. That normally starts a game of keep-away. When I uncover a mouse nest with babies, the babies get fed to the chickens. Of course, if you use poison, don’t feed them to the chickens.
The other thing that attracts them is a safe place to make a nest. Our coops and runs often provide safe places for them to nest. So try to keep the area as clean as possible. Don’t accumulate feed sacks for example. Don’t let trash build up. Keep weeds, grass, and scrubs cut. Just try to give them fewer safe places to nest as reasonable.
I agree, if you see one there are a lot more around and they are having a lot of babies. I suggest a very vigorous trapping campaign. I use that bucket trap and also set snap traps where the chickens can’t get to them. My coop is at the end of a 12’ x 60’ storage shed. There is no way I can keep that cleaned out enough to take away their nesting areas. I mainly try to keep the numbers down, I don’t think I’ll ever totally get rid of them. If I get a cat my wife will make a house cat out of it, that won’t do any good. I wish you luck on the rodent problem, that’s a challenge. But try to get them before the numbers build up any more.