I'm kind of sorry I missed this thread until now.
I've long had an idea for pirates based on the "Unbound" from The Last Angel series, or I guess the Reavers from Firefly are kind of a one system example. Basically a collection of outcasts, criminals, and remnants of destroyed/conquered races that don't have a permanent planetary home, instead wandering from system to system salvaging, looting, and attacking targets of opportunity. This isn't a perfect fit for Aurora, with its requirement for military ships to have maintenance, but I figure it's not too hard to imagine these races have an alternate design philosophy where they have military ships that are less efficient (IE slower/fewer guns/armor instead of shields) in return for being extremely low maintenance. Maybe that could even be a reward for dealing with them - chances to get an improved engineering space tech from the wreckage like you can/could get compressed fuel tanks from ruins.
The basic idea of how they'd work in Aurora would be every once and awhile a pirate fleet would appear from an unexplored jump point and wander around a bit looking for targets, including other systems. Their preferred target would be commercial ships or maybe undefended colonies, occasionally trying to take on very lightly defended stuff. Basically a reason to send a few escorts to keep an eye on your fuel harvesters, automated mining colonies, and such instead of leaving your whole fleet at the homeworld all the time, and a justification for why that colony in the middle of nowhere demands some defenses.
If they found a target they thought they could take they'd go for it with boarding parties/ground troops for colonies. In the case of ships, they'd fly away with them, on colonies they'd load up whatever they could in terms of minerals/installations/population and leave the rest, so it might not be a total loss. They'd then attempt to return to the unexplored jump point that spawned them before your forces could stop them, and if they did they'd despawn - the point being they don't actually have a permanent base to attack, they're just sort of the wandering mobs of space. This would both encourage spreading your fleet around - if you can hit them before they escape you can maybe grab your stuff back - and encourage actually exploring jump points before colonizing a system.
I picture their ships as kind of blurring the line between military and commercial - freighter like with light to moderate armor and a few light weapons. So slow and not a threat to a big fleet but possibly enough to overwhelm a lone destroyer or light planetary garrison, and the kind of ship that isn't practical with standard Aurora mechanics but makes sense if they could have military ships with commercial maintenance rules - basically freighters with a few guns bolted on if we imagine the rules allowed them to only need to maintain the guns.