1 - The problem with the first match-up is we haven't seen enough from either kage. As powerful as Hashirama may be, the third might be able to take this. Speed is a huge factor in this match-up and we have no spead feats for Hashirama. I think the 3rd might be too fast for him, and I'd say he could outlast him.
2 - 2nd Mizukage takes this with ease. Tobirama has nothing to hurt the 2nd mizukage with. Remember, Bringer of Darkness and the tunder sword were anime only. Tobirama's water jutsu are useless because of the Mizukages hydrification technique. If the Mizukage gets his genjutsu going, its over for Tobirama. He may be able to find the clam, but how will he destroy it?
3 - Is this a prime Hiruzen? We dont know what prime hiruzen is like, and in his old age, I cant see him defeating Mu.
4 - This I'm not very sure about. Wouldn't the Kazekages Iron sand/magnetism screw Minato's FTG technique (the kunai would just get pulled towards the iron sand). Not sure!