Rules of thumb are just guidelines, certainly. Going by the 4 sf rule, I myself have about 4-5 more birds in there than I should. They do okay, but the moisture from the poop and respiration of that many will make the ammonia worse and harder to deal with. I've found it much harder to keep the smells down and mine do not stay in the coop during the day; they freerange most of every day. Just depends on how much work you want to do daily, really.
Cant comment on a concrete floor other than be sure it's smooth. Very rough concrete may lead to abrasions and in turn, lead to bumblefoot infections.
Cant comment on a concrete floor other than be sure it's smooth. Very rough concrete may lead to abrasions and in turn, lead to bumblefoot infections.