I don't have any particularly strong expectations, as I've seen a lot of different ways of handling things. With that said, I do have a recommendation regarding material for what you could include - look at the species and cultural traits in Synapse, as well as the needs. Between the lot of them, you'll probably be able to fill a few holes you didn't even notice until then.

How do they differ from humans? Are they Star Trek style, where Klingons and Romulans are very much like humans with cultural differences, or something more like the Hivers from Traveller, which are physically and ideologically quite alien. Do they admire elements of other cultures and seek to share, integrate, copy?  I always loved the picture of a Kleibor in an Hawaiian shirt from Pacesetter's Star Ace, which instantly tells you a lot about that race.

Most of all, how do they fit into the game setting? Not so much from the point of view of a grand, beautifully detailed background awash with picayune minutiae, but from an in-game perspective: you've given me a great race, but how do they fit into the dynamic of the setting, dealing with different species or opposing political leanings? I'd also love to see more races which avoid the "desert planet" trap: there's a tendency in sci-fi games to have a desert world, a water world, a forest world... planets should be far more varied than that and too often races are presented in the same homogenous way. I like to know about the variety and conflicts within a race: the good Klingon, the friendly K'kree, the non-annoying Ewok...

Thanks for the responses! I will definitely it all in to consideration as I finalize my book.