Not exactly questions, everyone knew where Leyton was. Indeed, it's a plot point that he's frequently hounded by reporters, journalists and historians wanting to interview him, which he ignores.
Indeed, when Section 31 files were leaked to the public in the litverse, Leyton ironically ended up being one of the cleanest Admirals from recent times in that he had absolutely no connections with Section 31 and attempted coup aside, was not corrupt at all. Indeed, the reason Leyton got as far as he did with the coup was because Section 31 was too busy dealing with other Starfleet Admirals who were red-flagged as greater threats.
Also, according to the novels, the coup was motivated by Leyton's genuine belief that the Federation wasn't ready do deal with the Dominion. With that in mind, he would not have been able to be planning it out any longer than a year and a half, the amount of time the Federation was aware of the Dominion prior to the episode. And probably less than that, since he presumably didn't start thinking about a coup until after Jaresh-Inyo began rejecting his recommendations regarding the Dominion.