yes you are right and I didn't oppose it. when I say that "Mikey was planning to have Tony killed all along" I mean he was doing it through Junior, trying to turn him against Tony and eventually helping to manipulate Junior into the attempted hit.

as for Mikey P's motivations, Michael Corleone told us - in the novel, not in the movie - that they had to be personal as much as business. at least he wasn't beaten up over a civillian and in front of other made guys, like Ralphie was, but Mikey a made man himself would never sit with that and would always hold a vendetta feeling towards Tony.