Ships
Having fleets is crucial to having an empire. Theres nothing worse than seeing Loners without any fleets and having occupations(unless your the occupier). But What I think is that the more ships the better. Note the amount of credits it cost to build that ship is the amount of "ships it adds." So buying a Heavy Cruiser is 500 credits, it basically adds 500 ships to fleet, just fleet strength not actual ships.