There isn't much of an issue with the med blocker for cocci, but I still would rather not feed it to hens in any great amount or with regularity.
The chicks having cracked corn and grains will need grit to work that coarse stuff through their systems. Also, you've lowered the protein and mineral content of the commercial feed considerably. If half the mix is 8% protein grains (oats, corn, etc) and half the mix is 16% commercial feed, the result would be 12% protein, which is pretty low. I'd mix grains 1/3 into a 20% protein feed and achieve a protein blend of 16%. That would be what I'd do, but YMMV.
50 lbs of what is essentially scratch, mixed with only 15 lbs of feed would result in only 10% protein.