Nice variety. It will be hard unless you special order but I would recommend trying to get them as chicks within a few weeks of each other. We did the same thing when we got started- cobbled together a great variety of breeds in our backyard flock. Because we got them all as chicks and had them in the brooder for a good while together, we never really has any issues with pecking or bullying new birds. We even had a few bantams in the mix (we cheated them a few weeks older so they were approximately the same size.) If you go the route of older birds you will have to 1, introduce them in pairs or trios to limit bullying, and 20 either go through a quarantine process or risk introducing something to the rest of the birds from the new additions.
