I would like there to be an informative tooltip from the 'Attack Enemy Fleet' button or whatever it is called (The one between Colonize planet and Invade on the fleet action component). I really only want the MP of the to-be-opposing fleet but I wouldn't say no to more, and maybe as simple bar graphic or threat assessment would be preferable.

You mean a mouseover graphic like the one showing the chances for the automatic fight? Yeah, that would be fine.