I use medicated chick starter, since it's all I can get here, unless I switch to a grower/flockraiser feed. I'm careful to keep their brooder clean, I don't overcrowd, waterers, and feeders are cleaned daily, and temperatures are monitored regularly. Chicks are checked over at least twice a day for pasty butt. Fortunately, I've never had to deal with coccidiosis, but I check for the symptoms, and am able to treat it immediately, if needed.
As to eye color, I've never had a problem. Leg color is not to be black, but slate. The bottoms of their feet are to be pink(ish). No yellow. Mine breed true, in regards to eye, leg, and foot color. That does not guarantee that all of them will grow out to be S.O.P. Chest curvature, back curvature, tail angle and height tend to be bigger factors as to whether they are culls, or S.O.P.