I am just starting up with one hen and 3 teenagers that are leftover from my grandsons summer petting zoo he made with some friends. About 20 yrs ago we had a small city farm and I had about 15 chickens. As I remember all I ever fed those chickens were table scraps and scratch. I just scraped the plates after every meal and tossed it out in the coop. We had a good supply of eggs and never had a sick chicken. They had a modified tool shed for a coop and a makeshift chicken wire pen that was about 30x80 ft. to scratch around in. I never wormed them or mite dusted them or any of the stuff they recommend on this site. My only problem back then was racoons but once I got the shed racoon proof they were fine.
Now I live in Israel and the only chicken food I can get easily is scratch. So far thats what they have been getting along with the table scraps. I did cook up some quinoa and beans the other day and mixed it with ground eggshells and am giving them some of that every other day. Since we now live with my daughter, husband an 5 boys there aren't always enough leftovers for the chickens..LOL
I'm sure my advice is not scientific but so far its worked for my chickens.