We have a very small flock of 7 4 week old chicks. I'm looking to get some Silkie chicks or some Bantam Frizzles.... The question is: Should I get chicks that are older than the ones we have (so they will be bigger/the same size) or doesn't it matter? We have 2 buff orps, 2 Barred Rocks (one a roo, I think), 1 Ameraucana, 1 RIR, and 1 Black Sex link. TIA!!