Anyways, do you guys need something else to work with?
I have a rough skeleton for what the background story of this RP would be.
It's tentative and that's why I'm waiting for everyone else's civ profiles but here's a few bits of information.

The common dating system is Star Calendar, abbreviated as SC.
It was devised by the Terran Federation (predecessor of the Terran Empire which later became the Galaxian Empire)
It takes the old dating systems on Earth (24 hours a day, 7 days/week, months, 365 days a year) as standard.
The beginning of Star Calendar or SC0 is unknown, but theorized to be after humans developed interstellar FTL travel.
Because at one time the Galaxian Empire controlled the entire Milky Way, the Star Calendar got widespread.
Humans and even many alien civilizations still use it, albeit others came up with their own.
Still, it isn't rare during trade&diplomacy to discuss dates according to the Star Calendar.
Yes, this is kind of for the convenience of us, players.
The start date of this RP will be somewhere around SC5233.

Another is about humans.
I do plan to mention most of these in the Empire's profile but basically humans in this RP aren't exactly like us. Their genes were tampered with, making them somewhat more adaptable to the environment, more resistant to radiation and few lucky humans are also born radically tougher or faster than normal. In addition humans possess "excess chromosomes" and other modifications to allow them to crossbreed with almost every humanoid alien. These hybrids retain the properties and unique features of their alien half yet being recognizably "human". Yes, in short I'm giving a lousy explanation for the common half-alien Sci-Fi tropes.
Another important note is that humans are extremely numerous in this galaxy. The Galaxian Empire once became the only power in the entire galaxy, spreading human settlers all across the Milky Way. Thanks to a certain event which temporally kicked the population growth of humans to insane levels a large portion of the habitable planets were filled with humans, making them the largest humanoid race in the galaxy. The Empire declined since more than a millennia but to a lesser extend this tendecy still holds. While not as populous as in the current Empire, there are still about millions of humans per planet at average.
Wherever you go encountering humans is quite likely.
Of course it doesn't mean that every planet is owned by humans or they form a considerable population.
There are still many planets held by other alien races. A number of these may be even xenophobic against humans so there are planets without them.
But this gives you the chance to form your own kind of human civilization that developed after the old Empire's fall. (circa SC4000, you have plenty of time).

So yeah, keep these in mind.