Should be fine to stay the course as far as feed. Lower protein % might be slightly cheaper, but you don't want to drop below 16% which is usually what layer is set at. Lower protein % may increase odds of feather picking but there's not a magic cutoff to predict that.
Grit, they don't need a lot of it and not very often, so it may look like the container doesn't go down at all, until you realize it needs refilling again.
Oyster shell, your pullets are 16 weeks old so I'd start putting out a dish of it and let them explore it. They will eat a little out of curiosity at first, but shouldn't really crave it until they're close to or have begun laying. I just leave oyster shell out full time, whether we have chicks or whether it's winter time and no one's laying - they don't eat it if they don't need it.
Grit, they don't need a lot of it and not very often, so it may look like the container doesn't go down at all, until you realize it needs refilling again.
Oyster shell, your pullets are 16 weeks old so I'd start putting out a dish of it and let them explore it. They will eat a little out of curiosity at first, but shouldn't really crave it until they're close to or have begun laying. I just leave oyster shell out full time, whether we have chicks or whether it's winter time and no one's laying - they don't eat it if they don't need it.