I have a small fock of mixed breeds:
- 2 Silkie hens
- 1 Buff Orp hen
- 1 Barred Rock hen
- 1 Cochin hen
- 1 Welsummer hen
- 1 Golden Comet hen
- 1 Buff Brahma hen
- 1 Sebright rooster
The ONLY time I had any issues us when I stupidly added just the Welsummer. If I'd had half a brain, I would have added at least 2. Poor thing is neurotic, even though she was raised and integrated by a broody. I've not had any issues with mixing breeds at all. I have often thought that it has to do with the fact that they were all raised together, so no one ever stood out for looking differently. I added 2 Silkies because I was worried they'd get picked on. They are completely fine!
I started with 4 (Orp, BR, Brahma, Cochin) added 1 (Welsummer - BIG no-no and lesson learned!), added 3 (Silkies and Sebright), added 2 (Australorp and Comet - rescue hens I added as adults). I lost the Australorp recently...
This spring, I'm adding an Easter Egger, a Swedish Flower, a Sumatra, and a Polish. I like my yard candy and all the different personalities! None of these can really fly *except* the Sebright. But he stays put with his girls. They are all pretty mellow (besides the crazy Welsummer). The calmest and quietest are the Cochin and the Orp. Friendliest are the Silkies and the Brahma. The BR is amazing. Healthiest, smartest, easiest, and sassiest. I HIGHLY recommend!
If you have room, and I trust you do or you wouldn't be expanding, get whatever you want! Just integrate slowly. I agree about partitioning off part of the run while you integrate. Worked beautifully for me. I have a large run (though I wish it was larger still) with 3 feeding stations and 4 watering stations - just because it keeps them busy and gives everyone a chance to eat without the interference of chicken politics.
While integrating, I let them all forage in the yard together and put them in their separate areas of the run at night. Newbies always have their own coop (I use a small one (3 ft x 3 ft) I made for an isolation coop until they are big enough to hang with the big girls. After about a month of side-by-side in the run, I integrate them by taking out the partition and putting them all together in the coop at night. I've not had much problem... except the Wellie....
Good luck! Let us know what you decide!!!!!