they don't need to be real fleshed out factions just interesting enough to stand on their own or at least have a decent playstyle gimmick that separates them from the rest.
Alpha Centauri has several examples of this. everyone is "human" except the two aliens but the Gaians can steal mind worms before anyone else and thus tend to focus on psi squad combat very devastating meanwhile the nautilus start IN THE OCEAN and while that sucks it also gives them ample time to cut everyone else off from the sea. and a bit of self promo The Airborne Algorithm start with a needle jet and supply rovers making their early game very important as they explore and steal resources from places they have not settled yet.
for etarwars they could have 2-3 sith factions. 2-3 jedi factions. all with focus on cannon teachings but with a line of text somewhere in the faction bio that amounts to "well these guys are a little more aggressive about it"
EDIT: just thought of a better example. Sins of a Solar Empire. you have 3 factions and each faction has 2 sub factions. amounting to aggressive vs defensive
