Learn to cull.
Once you get the birds or hatch the eggs and grow them out, do yourself a HUGE favor and cull (rehome, sell, place, eat) any birds that are just not what you wanted to have in your breeding flock, or that are too small, too big, wrong color, too small of a crest, wrong color eyes, goofy comb, light colored legs, (or too dark) or don't look like the breed standard. Even if you never plan to show, it is a good idea to breed as close to the standard if you are keeping purebred flocks.
I have nothing against mixes, and keep a couple of intentional mixes myself. Right now I have a small batch of eggs in my incubtor that are English type Orpington rooster crossed with a few mottled java hens. I will hatch them in a separate container, and mark them, and house them separately so that no one ever buys one from me thinking it is a pure orpington. I would hate to get yellow legged orpingtons show up in someone else's flock. It will take at least two generations to breed out the yellow legs genes, and keep the mottling. None of the black hybrids will leave here as anything other than "mixed layers" to their new, non-breeding homes.
Another project I have just penned together is this EE roo over two coronation sussex hens, to make HUGE, gorgeous dual purpose EE's. That project will take a few more generations to get right, and it will just be "easter eggers" when I sell the offspring. Like I said, nothing against crossbreeds, but give correct info to the buyers, not as in the example above, "coronation ameraucanas" since that gene causes white legs, which can never be an ameraucana, since the breed standard is for slate legs. Here's a peek at my EE project roo.
and one of my coronation hens.
Only you can decide how close to the standard you want to breed, or how much you want to spend to obtain good breeding stock. Even "good breeding stock" produces a high number of culls if you are very picky about how you want your birds to look, or their eggs.
