You can still get 'purebred' chicks from a mixed flock (for each breed for which you have a roo, that is, although that may be only 1 breed). You can periodically isolate hens (isolation is unnecessary if you only have the one roo, of course) and then put the same-breed rooster in with them til you've got as many fertile eggs as you want, for hatching. Then dump them back out. It may add an extra wrinkle into flock dynamics but people do it a lot, it seems.
Pat, probably going to be doing this next year when the chicks coming next month are grown
Pat, probably going to be doing this next year when the chicks coming next month are grown