the one who controlled the mizukage was probably the real madara.
Well, current Madara has white and grey hair. Obito already has long hair, as we can see. Who knows.
As far as black Zetsu? He probably wasn't made until later. I like the idea of the whole "Zetsu Battle Suit," as it explains how Obito was so tall.
I think Obito will see Rin die, activate his Mangekyo Sharingan, and thus, Kamui. Filled with rage and hate, he agrees with Madara and keeps his plans going after Madara's death. Shortly after, Tobi attacks Konoha after practiceing the Sharingan, Kamui, and Genjutsu. It was several years between the Shinobi world war and Obito's attack on the village.
As far as Zetsu brainwashing Obito? Nah. People are the most easily conned, lied to, and in this case, manipulated when angry, scared or the like. All these years are enough time for someone like Obito to turn evil. See what happened to Sasuke throughout his childhood. Obito probably went through the same.