UI:

While selecting multiple fleets, their actions don't get displayed, the suggestions would be: display all actions available to selected fleets and add at the popover the quantity of fleets available for the action, maybe also inside the popover the fleet names?

Make systems management its own tab? its quite confusing to find the economic tab the only one with multiple options, or is the intention to add a populations tab to the senate later on (populations|elections tabs). Maybe use tab to switch amongst them?

Maybe this is a "to be implemented" feat or a bug but I can't visualize modules icons from the ship overview, all I see are light blue circles.

Clicking on a star system name owned by other player open a negotiation screen with him.

Technology:

Secret hangars tech (T3 or so), prevents other players from knowing the content of currently stationed ships (perhaps with some limit?)

Make forced truce a pacifist policy