I was ok reading that you had 2 BOs and 2 BRs as they are LF similar in size and temperament - but was not okay reading that you possibly will be throwing in 3 gentle-smaller Polish/Silkie crosses into the mix. Polish and Silkies are way smaller and timid than BOs or BRs and will get mercilessly picked on when all the birds reach full maturity. And if you have only one cockerel in the pen with the rest being ladies he will be chased and pecked to death. Hens gang up on lone roos in a pen. If you're going to breed him then only let him have one lady at a time in a breeding pen away from the others. Nothing wrong with pre-fab coops. We keep ours covered with a tarp to protect from sun and rain damage and keeps the pen floor dirt dryer in inclement weather. As your ladies start getting really big (6-7 lbs apiece) you may find them wanting to get out and free-range the yard. After a month of keeping our first 2 Silkies and 1 Leghorn we started letting them out for supervised free ranging. After another month we realized they were quite hardy even hiding from the Cooper's Hawk. So we planted a couple rose bushes, set up a few low lean-to shelters, a recycled doghouse, and a popup canopy (legs buried a foot deep in soil to keep from parasailing away) in the backyard for hiding places for them. They've been free-ranging for 3 years now and only use the coop to lay eggs and roost at night. They're real good at sounding the barnyard alarm when the Cooper's Hawk visits. He won't go after hiding hens. Hawks prefer to swoop down in open grassy areas and the hens know this and hide.