Garden planets, rare and sought after specimens. Only a few species have more than a handful. To discover such a lush living thing is extraordinary luck. Only the Agrarians, a small ancient species that are masters at growing all living things, live exclusively on them.
Gas giants, not as rare but almost as important. Mostly the Dregons call them home, swimming around in their gaseous interior. From within they bring forth all the fuel a system needs and more. A system doesn't really come alive, until the Dregons have moved in.
Now garden planets might be rare but there is a saying among one of the species, "You make your own luck!" Although generally not as good, terraforming planets have long been a staple for intergalactic civilizations. Almost all species found in the galaxy lives this way. Filling up systems to the brim. It`s a slow and arduous process but necessary for all but one.
The cold void of space, most fear it and rightfully so. A single mistake and you not only kill yourself but most of the people around you. Only one species is insane enough to live in it and call it home. No marvel of engineering, no magic saves them, only stubbornness. They suffer just as much as anyone else when living in space, losing millions every day. Yet they persist.
They are the Humans, traders of the galaxy. "We choose to do this not because its easy, but because its hard", such stubbornness is what defines them. They construct rings around worlds, to live in and trade with the planet below and beyond. "Marrying the system", as the humans call it.
Doing this, they binds us all together. It is said that wherever civilization go, humans will follow. To build a helping hand, and connect it together with those back home.
Giving rise to the old saying, "It doesn't matter how full a system is, there is always room for humans".