Can I mix all of this?

That's exactly what I did last year for my flock. This year a switched to flock raiser because I added a dozen, now 12 week old chicks, to my my older 1+ year chickens, one duck. When the youngens get about 16 weeks I'm going back to layer pellets and some scratch grains. IMO the scratch I get has enough cracked corn in it. I'm thinking about a 2:1 ration (2 parts pellets/1 part scratch grains) because scratch for a chicken is like feeding candy to a kid. LOL!!!