I buy layer pellets and a high protein grower, both in 50 pound bags. I have a plastic garbage can that I bought new for the purpose of storing feed, and have husband hold one bag while I hold the other and we dump it in at the same time to mix it. So everyone gets the same thing, mixed. If my babies are old enough to live with the big girls, they're old enough to have mixed feed.
Haven't had to add oyster shell, I have it on hand for any issues, but right now my shells are perfect. I was adding it from the start on my last flock, but my eggs had issues. Thin shells, soft shells... things I hadn't seen before. This time I haven't added it, but I bought it anyways just in case. No issues, no supplements.
I also shop the mark down rack at the produce store to get them tomatoes and greens.