I believe you are referring to the fan like thing which resembles the uchiha crest, i believe it is a fan like weapon of some sort .he probably wears a mask coz he has some damage to his face or if he is not really madara then to hide his identity
that 'thing' that hangs behind him is a weapon of mass destruction that no one knows what it does or how it works yet, but if Madara has it, it's gotta be awesome! and he always wears a mask because that's how Kishi drew him.
no. his face is going to be shown in either the final battle of the war or near the final battle of the war; when he fights Naruto, Naruto and Sasuke, or Kabuto.