If I had to do it all over again, I would start with chicks straight from a breeder or a healthy farm.
Alas, I went and bought 6 second-hand red stars not knowing that that breed quits at around the age I bought them so even when they started laying again I was lucky to get 2 or 3 eggs/day. So, what do I do? I see an ad for more of these red hens for $1/each, poor old man had wound up in hospital and his flock had to go... Right price, right? So I bought ten and took the rooster. 2 of the hens I busted eating eggs so they had to go, several died of mysterious causes, then in the winter the coons took care of a few more (probably weaker ones so no big deal). Anyway, for all the money I spent (mostly in gas to drive out to these places and feeding hens that weren't producing), I never got the nearly the amount of eggs from these birds that I should have gotten and I think I wound up contaminating my coop and my land with whatever these birds were carrying.
So, this past spring I bought some purebreed australorp chicks from some private farm (non-registered breeder). 7 of the 8 turned out to be boys. The girl is proving herself as an excellent layer but she has a funny cough and a lot of her eggs have blood spots... Inbreeding? Probably. The woman I bought them from buys hatching eggs, incubates them and then sells them... so where are her eggs coming from?
My best and strongest birds that I have now: the 3 remaining red stars (out of 16 that I started with a year and a half ago), only one of which is still laying; the ameracauna crosses that I bought from an organic free-range farm as pullets and the houdan/dorking crosses, also bought from an organic free-range hobbyist. 2 of my roosters are also in excellent health, the third has an occasional cough similar to his sister's.
My advice: don't be in a rush like I was, take your time and be very selective of the birds you buy. Once you bring disease or other pathogens onto your property you may find yourself with more work than you planned on! Also, my experience has also shown that purebred doesn't necessarily equate to quality and vigor, as my best/healthiest birds are all hybrids. And beware the production "red" or "brown" layers, aka comets, stars, RIR - they're designed to lay loads of eggs but only for a year or two so they are not bred with health in mind! (At least not where I am.)