The box call and the slate call are the two easiest to master I believe. Get the basic sounds down and you should do fine.
You do not need decoys....sometimes they help, and sometimes they dont.
Most any call will be ok to start with, they key is to practice, practice, practice. You want to master the basic sounds and then move on from there.
Try to find areas where the leaves have been scratched away, feathers around trees (roosting areas), turkey droppings, turkey tracks, dusty bowls where they like to dust themselves. Once you find their roosting area try to find where they are feeding, and strutting. Once you have done that you can try to find the way they get from the roost to their feeding areas.