Hey Pup,
I use pigeons to train a Springer, so I cant really help you on how many you'll need. I know I always have 2-5 on hand just about all year round.
I just have a 4' x 4' x 4' pen with a roost, and with this size, I can keep 4 or 5 for a week or so before they lose their strong flushing abilities, something important for springers but not for britany's. The bigger the pen you have the more birds you can keep, and the longer period you can keep them.
Mike