Was planning to do some concept art for the other races and here are my thoughts.
Humans- not much here.
Pirates- not much either, but they should be distinguishable, how bout humans (federation etc.) all have a uniform, some colour palette or something, while pirates are just random "pirate" clothes?
Robots- (need special name?) Could be like more machiney instead of human shaped, boxy but still advanced looking. Should have a logo or colour scheme for each race too(worked for FTL ships).
RAI- I thought these guys could be like human shaped but all metal and wirey, but definitely like a human. And I thought... chrome... with a glowing red bar for the eyes...
Spiders- Simply spiders, but since they've evolved to be intelligent enough for space travel they should be upright with refined features, so they seem a big step up from just spiders.
Now for the fire, energy, rock metal dudes we could have just two races instead and have
Energy- About speed, lightness, sleek. These people could then still have fire and air and water versions which would be neat, but I think just energy would work. These guys are rivals (not archenemies but rivals) to:
Mass/ or Matter- these would have the rock and metal versions. Would focus on toughness and be bulky like. If these guys are singular races then I propose one more race.
Clowns- Jk
(Sorry srul

)
So the story is that a group of humans found some sort of superintelligent goo, it merged with the humans, using them as a vessel to spread their physic ways and conquer the other races, maybe it shows up in late game sectors. It'd be kinda like slugs. But more malevolent and all knowing.