Andy, throw some fine grit down, maybe in their food or on a sheet of newspaper.
Recent studies have shown that adding grit from the get go helps the birds develop better digestion, which aids maturity. Especially important for your meat birds of any feather.

For mortality, most of my birds have croaked when older and out on range. I haven't lost any chicks in 10 broodings.

I lost one turkey poult, but he was noticeably sick when I brought him home.

My cornish cross meat birds have weighed 10 lbs! (14 week old roosters, butchered), which is an enormous bird. I cut up 6 of those peckerheads and ate the wings. 4 wings were a meal all by themselves! Our family can eat for a few days on one of those carcasses.

If you go with meat birds, you might want to look into building a Whizbang Chicken Plucker. Google and youtube it, and if you're interested I'll send you the plan book.

it makes butchering go a lot faster when you've got a auto plucker. I can do about 7-9 per hour.