3) Not long after the Havana operation fails, Roth and the Rosatos are "on the run." As I already noted, this changes the whole dynamic of the situation for a would-be traitor. That is, you don't try to kill your boss for another boss, when a) your boss is now back on top ("Michael, you've won") and b) the other boss is on the run and unable to provide you with the same incentive to turn on your own boss as he could previously.

4) If, as I believe, Rocco was the man helping Roth, he would not recruit his own men, with all their "machine guns," to help him kill Mike. Why? If he approaches one of them and makes this proposition, he gives the guy he makes the proposition to an opportunity to replace him as Caporegime. This guy will pretend to go along, and then go straight to Mike with this information. Nothing Rocco could offer him could outweigh what Mike would do for him in return for this information. Machiavelli puts it well when speaking of men who want to recruit others to kill a tyrant: "as soon as you disclose your intent . . .you give him the means with which to become content." [Addition:] This, I presume, is why the two guys who turn up with their throats cut are not men who were part of the compound security detail.