There is so many things to select for. I want what I want, and have said it enough around here. No one wants to hear it again. But, do not get to caught up in it. They are chickens. Kill the man fighters and any bird that is a nervous wreck compared to the other birds in that same flock. These things are heritable, and they do matter. Just be careful about getting stuck on this point. We do not want birds that are lethargic. We just want to avoid extremes. Let them be chickens.
Concerning calm and fertility. I am not so sure about that, less extremes. A good active vigorous male is going to top more hens. If that is what they are saying, maybe. And that is what you want. We do not want lethargic males. We want them active and vigorous. We just do not want man fighters. We want to avoid extremes.
The breeding pens are as varied as those breeding. I have a variety, and had different things in mind at the time. What we are trying to accomplish is to move a population of birds forward. We can do that with small and large groups. Many or few groups.
One of the best breeders that I know of simply runs two families, and keeps about ten females in each family. He keeps about four males. Another keeps a single group of 25 (plus or minus) females and rotates a single male on them, and keeps four or five males. Neither of these are using many small pens. I am sharing this to say that it is not a requirement. Both of these have the best birds in that breed and variety in the country. No matter what we do, it will still boil down to selection. There are advantages to every style.
I am afraid that we over emphasize methodology. I do.
I do not like pvc pens. PVC does not hold well over time. I do like the bottom frame to be treated lumber, and pvc can be cut in half to fasten to the bottom. This aids in moving, if it is a concern. I am ok with 4'x8' pens for four hens if they are being let out. 5' x 8' is better for supplying shade, and they can be let out every other day. The eight extra square feet makes a difference, and the extra foot wide adds more shaded space. I like them three feet tall (32" without top and bottom plate), and a gable roof for at least half. The gables should be open. This provides more elevation, and gets the heat radiating from the roof off of the birds. I do not like metal roofs on these small pens unless they are in the shade in the summer. Small enclosures with metal roofs, baking in the summer sun, is not a responsible way to raise birds. In the shade, they are fine. An option for metal roofs, is thin sheet insulation installed before the metal panels. The cost is negligible considering, and makes for a cooler enclosure.
I have large walk in tractors that I love. They might be too difficult for some to move. I use wheels, and a hand cart. It works well, and I like walking in them to feed, water, and collect eggs. I let them out every day, so it can sit stationary for a while, if need be. I can keep a dozen hens in these 8'x10' pens, and not let them out daily. I still do though. They work best if they are on clean grass all of the time. They all work best if they are always on fresh forage.