There are purebreds. Then there are the crossed whose background include a mixture of several different breeds. These also may come in different sizes. And lets not forget the mutts. These generally have unknown ancestry, but are generally problem free, making a good family flock.
Most people buy chicks in the spring from a hatchery.
Most show poultry are obtain either as hatching eggs or adults as pairs or trios. Roosters are not needed unless you are going to breed. If just eggs is the goal, then a rooster is not needed. Hens will lay very well without a boyfriend in with them. Half the fun of keeping chickens however is watching him interact with the hens, and listening to their crow.