And I remember those old threads saying Obito's new mask was because he was going to get a third eye on his forehead. Maybe that was his ultimate goal, since he had no plans of reviving Madara.
Naw. He was referring to Sasuke since he was attempting to bring him to his side and since, at the time, he needed a replacement eye. The fact that he unlocked the third eye later is unrelated.
No, the new eye he was talking about was the Rinnegan he had. I think most people missed the point in that statement. The reader needs to place Madara's statement in the context.
Clearly, Madara was comparing the Senju brother and him, and he was comparing two era: (1) when they were alive, and (2) the time in this war.
When they were alive, the Senju brothers were stronger than Madara. But now, when he was talking, not only he was stronger due to being alive, having Hashi DNA, but also because he had a new eye that he did not have in his previous life.
I am positive because Madara said he is not sure the eye will stick with him. If you consider that Kaguya had Byakugan, it is possible that Madara will lose the Rinnegan if the Shinju power wake up - which will turn his eyes to Byagugan. The only problem is what is the strength of Byakugan compared to Rinnegan? Don't bash that question because eye power can change depending of the knowledge and power of the user.
Nope. He was referring to sasuke which is why in the very next panel you see sasuke's eye zoomed in. Furthermore when he stabs sasuke he tells him he gave him enough time to decide which side.