I am apparently a "collector" - have 9 hens - only 2 are the same breed and they get along GREAT!!
There are lots of integrating tricks - space , distraction , visual introduction for a period of time.... others....
I have added hens along the way - had some trouble but hung in there tried different tricks 
and THEY figured out how to get along.   I noticed which ones are more docile breeds and made sure
I protect them as much as they need until the rougher breed assimilated .
I even have a tiny (tiny tiny) silkie who is right in ther with GIANT standard Cochins, and  Sussexs
she hold her own , has a stubborn streak and will not move if they want her to !   
I have been lucky so far!   
Good luck! Read lots !