I've had a mixed breed flock for 3 yrs and no problems. I love my Buff Orpingtons. The Barred Rocks are noisy. Araucana/Americanas are a little smaller & skittish - not very people friendly but lay beautiful eggs of varying shades of blue & green. My Buff Brahmas & Speckled Sussex succumbed...
My chicken mansion (as my family calls it) it almost ready. We're in the hot Texas Hill Country. Sand sounds like a great option to help manage the TX heat with easy clean up but it can get cold about 4 months of the year. So I'm thinking I'll use sand for the warm/hot months, clean it out & use...