Itachi was convinced Obito was Madara simply because of the effort Obito put into pretending to be him. Itachi figured out someone had manipulated Kurama to attack the village and believed only Madara could do that.
Kisame, on the other hand, met Obito face to face when he found out the Mizukage was being controlled. Obito willingly revealed his identity to Kisame as he found weakness in Kisame's lack of identity. It wasn't that Kisame believed he was actually Madara, but believed so much in Obito's crazy plan that he willingly called him Madara, being the loyal disciple he was. He was simply playing along with Obito's lies.
Everyone knows that Obito's right side healed fast because that was the half of his body made up of Zetsu cells.
Zetsu's statement about the 'insides' are doing well wasn't about Obito.... it was referring to Yamato. Spiral Zetsu had taken the hostage Yamato's body in order to enhance his wood jutsu skills. That's what Zetsu meant.
Kurama saying 'you' was just another way for Kishi to convince the audience that Tobi was Madara. Kurama could have simply been fooled by Obito, it doesn't confirm anything. In addition, the statement was so limited he could have meant anything. Perhaps he was going to say: "You, with your manipulative sharingan, remind me of Madara Uchiha." This would have been similar to his comparison of Sasuke to Madara when Sasuke got inside Naruto's psyche during their fight. His statement was cut off because Obito was taking full control of him.