I agree strongly with Lordcluck's advice. Unless you intend to show your birds, you will probably not be too worried about the finer points of conformation, therefore you will probably be happy with 'pet quality' birds that look pretty but wouldn't make it in the show world. But you do want to know that any birds you buy are healthy, have been well cared for, and not exposed to the stresses of a move to what in many cases is an unsuitable outlet with non-specialist keepers for the birds. Moving home is stressful for chickens at the best of times, it depresses their immune systems, and it's common for birds to go down with illnesses thay might have avoided if the introductions had been done carefully and stock had been sourced directly from a reliable breeder, without any move to somewhere else in between. Any additions you make will need to be kept separate in quarantine for 2-3 weeks, and also introduced carefully to avoid bullying and stress. Also, this is perhaps not the best time of year to be buying new chickens, - maybe get the birds you have now through the winter, all the rain, cold, snow, winds etc, and see what you feel like doing in the Spring, when maybe you could consider some chicks.