Chicks need chick starter and really nothing else. Guinea Fowl need chick starter until about 3 weeks. Then a mixture of game bird and starter until about 5 weeks. After this, Guineas do better on straight game bird feed.
Chicks can start a mixture of poultry grain and starter about 5 weeks of age and after 8 weeks they can go in with the "big chickens" as free range and eating whatever they eat.
Guineas do not do well in a "flock" setting until about 10 to 12 weeks of age. They just seem to be babies until then.
I have 10 week old Guineas that have JUST started to defend themselves in the flock. Before this, they were avoiding ALL the other birds and running for cover.
Now, they are being excepted into the "gaggle" and are starting to run with them.