Well, to start with TB, I disagree about Michael's "looks". I don't see those looks at all and it was Fredo who initiated the knowing people in Havana conversation. FFC had Fredo bring the money to Havana to give Fredo a segue into the Havana scenes.

Of course, some will always struggle to know why Michael told Fredo anything about his plan to murder Roth if he suspected Fredo. For me, part of the answer is easy: Michael didn't suspect Fredo (there were no "looks"). However, Michael really didn't need to tell Fredo anything about his plan.

You're no doubt right about Michael's arrangement for the plane to exit Havana. Given that Michael revealed to Fredo that the Cuban military would carry out his murder, he probably needed the plane to immediately exit Cuba to avoid his own murder. I think that his failure to tell Fredo about the plane earlier was simply FFC's choice to add to the drama of the chaotic New Year's eve scene. But, Michael could not know of that chaos in advance, so why did he place himself in the lion's den? Remember, he leaves the party when he does only because he sees signs of Batista's collapse.