I can agree with this statement, "the man behind the mask is the man who knows everything". But this agreement can also be applied to Madara as well.
Tobi is very aware or is very knowledgeable in the NU. He knew about the SOT6P existence, his sons, the history of the Senju & the Uchiha Clan, their rivalries, the ten-tails, blah.. blah.. & so forth.
However, I disagree that he is Orochimaru. As I can remember, Tobi blamed Orochimaru for the power-ups he gave to Danzo. Moreover, one of Akatsuki's missions was to kill Orochimaru. So, it's highly unlikely that Tobi & Oro are one & the same.
I also doubt that Orochimaru is Madara or he was hiding in his body as like what he did to Sasuke before. Sasuke stated that he wanted to meet Orochimaru because he want him to do something for him. I kindly doubt that Madara will take Sasuke's words that seriously.
I think the very reason why Sasuke want to meet up with Orochimaru is because he is the only shinobi so far that have knowledge on how to stop Madara's Edo Version. I think Sasuke want to get rid of Madara too as he was shocked that he was still around even after Itachi & him stopped Kabuto's Edo-tensei.