Well, and forgive me if this was mentioned and I'm flaking out, but when we start with our characters, they will be Thralls, correct? 
Also, what exactly is the cast system? And is there a major plot at work here, or will it be mainly the lives of the characters? I'd assume the former, but you know what assuming does XD

I'll probably think of other questions as I think about a character, so forgive me if I never shut up.