We have 7 breeds, one male. Most are nearly 1 year old, a couple are 5 months old. No issues in getting along, and they all intermingle.
However, if you plan to breed them and sell chicks of a certain breed, then you should plan to separate them so that you know you don't have a barnyard mix. If it doesn't matter, let them mix. Selling eggs won't be impacted by intermingling either.
If you want to keep separate flocks, then you might want to give us some more info, like how much space to you have to make into chicken space? Are you going to use an existing structure or build? free range or mostly enclosed run (with possible supervised free range). How many chickens do you currently have - and/or - have you ever had chickens? Are you limited by an HOA or city restrictions on the numbers of chickens? Your temps aren't too bad in SW OH, but can certainly get cold, humid, rain, snow, and pretty hot/humid in the summers.
Last summer I visited an old rancher out west that sold their ranch and settled onto a 5 - 8 acre plot for retirement. They built their home and out buildings for their retirement hobbies including chickens. They were showing me their chicken building and it was a metal pole barn with a cement floor. Approx 20ft wide by 30 ft long. Human door on one end. Inside they had 3 pens with ladder roosts taking up approachx 100sg ft each (about 10'x10'). The back interior side was the access point for all pens, egg collection, feed storage, weather protection. Then a pop door in each to separate, side-by-side runs. They indicated they closed the flocks into the building during the coldest months of the winter, no outdoor access, but they were still separated. Anyway, seemed like a good strategy to me to keep flocks separate yet still easy to care for, in a relatively inexpensive build.
