I also use use Sevin-dust on the ground under ALL my cages. Also on chicken that have a severe mite/lice problem.
DE works in coop and covered run. but useless where it can get wet.
Been using Sevin in garden for 20 years+, on chicken 3 years+
3ft per chicken, more if you can, so a 9ftx9ft would be the smallest I would go. and a part of it needs to be kinda high.
The high part will be the roost, needs to be at least 6-7ft IMO
I love the Seramas attitudes. Huge ego but never attempts to attack/spurr any humans.
I am in the process of getting some Appanzeller Barthuhners also.
Turkeys grow at a lot slower pace then chickens. So most likely would get picked on and or killed. I would personally raise the turkey on my own and leave the chickens in with the other ones