You can mix turkeys and chickens. You'll need to introduce them to your flock like you would any other additional birds, and keep them separate until they are big enough to defend themselves.
They are much bigger than chickens - if you are getting heritage breeds, they tend to be around 11-18 pounds PROCESSED (so add in their insides and feathers and they weight much more) If you are getting double breasted turkeys, they can weigh up to 40 pounds.
Yes, they perch. IF they are heritage breeds. The double breasteds get too heavy and can't get off the ground. Heritage breeds like to perch, wild turkeys sleep in trees, and heritage breeds will want to do the same. They want to perch HIGH. You want to make sure your perches are strong.
They can eat the same feed as your chickens - grower ration when they are little. Double breasteds need to stay on grower ration their whole life. Heritage breeds can switch to layer ration when they are feathered out.
They can eat scraps, just like your chickens do.
I don't know if you free range your chickens, but turkeys can act a LOT different than chickens. They are more independent, and they want to do their own thing. They WILL seek out and find a tree to sleep in if you free range them. They can hop a LOT higher and further than a chicken and can get over fencing. It is not surprising for us to see turkeys on the roof of our cars, as well as our house. Chickens will stick together in a flock, turkeys will wander a LOT more, and will find where they want to sleep at night, and return to it each night. They may not bond with your chickens as a flock, but they'll do their own thing and be OK that way.