I agree, for dog training you really don't need to go to the expense and the hassle of breeding your own birds if you have a place to supply you with them. Building the flight pen, getting in your chicks every year and raising them up will be way less work and money. To breed you will probably need an incubator, and although I have never raised flight ready birds (I plan to one day!) I think, in my opinion, it would be too muich hassel to try to breed the flight birds themselves. I would keep separate stock in breeding cages to produce the eggs I needed to supply my flight cages. It would be a lot more convenient, and that way if I loose flight birds I am not loosing breeders. I enjoy raising birds and since i live in Canada there are very few places to get quail chicks in any kind of quantity, so i really have no choice but to breed my own (I can get pheasant chicks from one hatchery in alberta, but Quebec is the only place that does quail and it would take 3 days for them to get here - not good) For your purposes, and living in the states where there are hatcheries just about everywhere, it would be so much easier to order chicks annually.
I'm not an expert on flight pens, but don't they reccomend them to be at least 100 feet long? I may be wrong but it rings a bell. They also reccomend training on the same bird you will be hunting if at all possible.
I am quite excited to start training bird dogs one day - I just need to finish university and get a plot o land. I'm a professional obedience trainer but bird dogs are my passion - if there's anything I love more than dogs, it's birds