And just a note to the "but its not canon" crowd.. it is Canon...in its purist from.. all of the events in the trek series's happened in a civilian universe. And civilians do fight. Military types simply have specific training..and in the case of players.. are still IN the military.
The difference between a military captain and a civilian captain.. odds are the civilian actually OWNS thier starship, and isn't flying a government loaner out of the pool..
People who say "it's non-canon" in this context probably never saw the various episodes where we actually see freighter or raider crews.
In this particular instance at least two episodes of "Enterprise": "Fortunate Son" and "Horizon" come to mind.
Also TNG:"Gambit" as an example for mercenaries.
Some of the playable "individuals" might also come from a military background (retired, discharged etc.) so we could still have tactical as a profession.
Tinkerers of any sort would fill the engineering role.
Former sensor officers and prospectors looking for an astroid filled with valuables could very well allow us to keep the general class structure by giving us science-types as well.
And yes, in most cases those folks would have their own ship.
There could be freighters (large and slow ones, small and fast ones), raiders, mobile labs, scouts etc.
And they could be from different races from around the quadrant.
Some of them would probably be older military-grade ships, some of them a century or more old (wink).
So a creative raider group might operate a couple of old 22nd century Birds-of-Prey.
Maybe a Klingon has gotten a D5 converted to an armed freighter (like the one from Enterprise:"Marauders").
More adventorous people might get their hands on an old surplus Starfleet ship like the Oberth from TNG:"Hero Worship", or maybe prefer an old round-nacelled Romulan Bird-or-Prey with its plasma launcher replaced with modern sensors.
These people could of course do..dirty work for all sides involved in the current affairs and gain resources so the ships can be upgraded via different Rep sytems.
Some freighters might still run some century-old phasers that need to be upgraded to something more modern.
Do you buy disruptors from the Klingons you just helped with that illegal colony?
Or do you prefer to take a more modern phasers from Starfleet Intelligence after you brought them some intel on True Way fleet movements?