The fictional stuff to address:
In this setting, there's more organization of people and resources, big machines, big groups, big armies and ships. What happens when the characters face the equivalent of a star destroyer in their little putzy ship?
The easiest place to start, probably, is creating a quick size chart and saying one step up from you is a small gang, two steps up is a large gang, and three or more is effectively untouchable. You can't invade a world with a small gang.
To borrow from the army really quick, the scale might be kind of like this:
Soldier
Squad
Platoon
Battalion
Regiment
Division
etc
But maybe not quite so many, I dunno. But the idea, is, say, that a tank all by itself probably counts as a squad, with good harm and armor. A squad with anti-tank weapons could probably take out a single tank, yeah? A bunch of tanks would count as a platoon, maybe, and then it gets scary for the squad.
So a regiment fighting a battalion would be like a person fighting a small gang. A squad fighting a regiment would be like the squad dying in a bloodbath.