Interchanging characters within the same scene Will I be able to create an image with a static setting(a playground for example) and then be able to interchange different characters into the picture without having to recreate the entire setting?

Also will I be able to change features on a character (e.g. hair) without having to recreate the entire character?
Yes. You can control these sorts of things in many ways. You can use layers, showing and hiding objects, combining meshes into different objects, and of course Linking models from different files. It is a very broad area.