A small bit of backstory I had in mind as flavor:

A once-peaceful race living on the edge of the galaxy, the Vanaari held a deeply religious reverence for the vast, unending cosmos that surrounded their homeworld of Des'pynea, a world lit by very little natural sunlight within it's own solar system.  Largely untouched by the galactic upheaval throughout the rest of the stellar neighborhood, the Vanaari have lived a life of little outside contact.  Very recently, however, a burst of radiation from a nearby stellar collapse has wreaked havoc upon the peaceful Vanaari, burning away their physical bodies and fusing them with the very nature of the endless starry void they have so long since revered.

Des'pynea had been a mediterranian planet abundant with plant and animal life despite it's dark skies, but thanks to the cosmic cataclysm, resources are beginning to dwindle.  With what limited technologial resources the Vanaari have, the survival of their species now depends on branching out to their stellar neighbors for aid-  be it through negotiation, or by much more subtle methods.  

There's definitely some inspiration from Greek mythology in what I have in mind, especially from the goddess Desponia.  To anyone on the outside looking in, Vanaari society would definitely be a little culty.

Gameplay-wise, I would not think that the Vanaari have an outstanding military capability-  at least, not right away.  Military victory against fleets would need to involve subtle ways of weakning their forces before engaging, perhaps even turning the technology of their own ships against them, leading to engagements of a main fleet against a small number of hacked vessels.  Progression down the right trees could offer more powerful vessels of their own, perhaps based on earlier fights, and which fleets they'd been able to gather intellegence on to craft their own.