Your tin sheet will work fine. Just make sure it's sturdy enough to support the dirt on top when the pit is buried.
Take a weed burner to your hunk of chicken wire. It's not going to be touching the food and like Bob said, temps aren't going to be high enough to make a difference.
Like Bob's bundles...you just need something to hold the meat together when you pull it out of the pit. Baling wire is fine, just use enough to keep the pig from falling apart. Chicken wire is less work, but baling wire does the same thing.
There is no "turning over" of the pig once it is buried.
As far as buried, cinderblock or horizontal pigs. They are all different but danged tasty. Underground pigs are special, moist and tender, really hard to beat.
Any meat cooked in an underground pit is good, goat, beef, turkey, venison.. it's all pretty tasty.