I agree about the bantams. If you get them all as babies and raise them along with large fowl chicks, no problem. Introducing new bantams to an established flock of large chicken could well be a problem.
Also, if you were planning on getting chicks, and live in an area where roosters are not allowed, you might run into problems, too. Because bantam chicks are rarely sold sexed. Most of the time it is straight run only, though I'm sure it's possible to find them.
If you really have your heart set on bantams, maybe set up a separate coop for them if you can.