Regarding the question of the strongest ok the Kage level ninjas is this. Sandaime retired not because Yondaime was a stronger ninja than him, but because he felt that he was ready to retire, and his powers were on the decrease. The very fact that Sandaime matched up as well as he did against Orochimaru at the age he was at should speak volumns about the power he had in his prime. Orochimaru was as strong as he was at his prime, noted by the futility of Jiraiya's and Tsunade's attacks. (Orochimaru fought on par with them without his arms or jutsus, which should destory the notion that Jiraiya's stronger) But Sandaime fought on par with Oro with his arms. If you believe that Oro and Yondaime were close in strength, then you have to believe that Sandaime, IN HIS PRIME, was the strongest ninja. The thing about Yondaime is that he was so good, so young. He hadn't even reached his prime. He is similar to Kakashi in the sense that even at their current levels, they still have a lot of room to grow, or had in Yondaime's case.

About Sasuke and the Kage Bunshin. I would think he has by now, and certainly after the time skip... if he still exists.