2. It depends on how much of a free will Madara actually had, how long it takes to remove the control and if there is some kind of an alert when someone tries or even thinks about performing it.
3. Assuming that Sasuke spoke the truth about the criteria to obtain Susanoo, he still needs to showcase at least 2 MS jutsu, someone's going to die ;P.
The real question should be, why has he left the information about performing the jutsu ? It looks like all people consider it an atrocity (even Madara) to cycle of life, it's even hard to imagine Tobirama using it unless he was really pressed. Leaving it behind could backfire on the Leaf, which didn't seem too eager and as whole to this day, isn't eager to use it.
I think it's because the jutsu wasn't complete and it's real purpose is a true resurrection.