Different breeds are fine together, mix it up--have fun with it, it's what ever you want! By the way--Barred Rocks are great......I have 6 that I love and are great layers and hardy.
I'm going to say Buff orpingtons...we have 2 of them now and they are just sweet hearts and love attention. They are still way to young to lay, but I hear they are great layers and hardy too! Good luck.
This is Stella and Eve!