These can either be used individually as their own dimensional seeds, or as part of an overarching setting. For those familar with Chronicles of Riddick, or Flash Gordon, or one of a dozen other stories, the underlying concept is simple. There are a large number of independent planets with limited interstellar travel which are colonies of Earth, or humanoid aliens. Each of these colonies is dominated by a certain 'style'. As an example, Riddick is a Furian, and comes from Furia. Furians refuse to be dominated, and tend to be physically impressive to enable this goal. Now, the Chronicles does a good job when it has one of the villains repent and reveal he is a broken Furian. Because people are people, and breakable at times.
So, lets make our collection of worlds.
First, bubble drive creates a miniature universe surrounding the spaceship in which the minimum speed of any particle is 10X c in the exterior universe. It also lessens inertia by a hundredfold. This requires ships to be literally tied together as screws will unscrew themselves with ridiculous ease. Even then, the molecularly sealed 'rubber bands' and 'duct tape' as the two primary sealants are colloquially named, have to be tightened and resealed before every flight into the bubble verse.
Also, sometimes strange, hallucinogenic visions appear to star travellers. This is part of the reason most passengers ride in a state of drugged stupor to keep them from receiving messages, and doing things at odds with the survival of the ship. Some famous ship disasters and mutinies occurred before this policy of sleeptravel was enacted.
Also, some of the planets that were colonized were fundamentally changed by the visions some of their passengers had.
The problem of terraforming:
============================
Most of these types of settings have a problem with terraforming. They show little to no serious signs of being terraformed. Maybe they have a few devices scattered on the surface, but its not enough to be believable. They then toss in dessert environments, and expect you to believe that terraforming is rather simple, but only partially done instead of something that would take mass, concentrated effort on a scale as to totally dwarf the colonization and industrialization of America.
You can just handwave, and stipulate that there are dozens of habitable planets out in the galaxy. Or you can mention something about a Terraforming Service in the last century (of which there are no remains...). I'm modifying an idea from the Foundation series.
Early in the starflight program, no human or even anything above a unicellular organism could survive bubble drive. This lasted for nearly two hundred years until Sir Rop Smith invented the 'intrauniversal modulator'. But there was a far-sighted man, Saint Alex Chancellor who founded a religious order....The Order of Saint Appleseed (based on the stories of Johnny Appleseed). This order sent out robotic exploratory vessels loaded with bio-packages full of various types of cunningly designed bacteria which would be released according to a planned program.
There are stories that when the Saint died from an assasin's bullet he said 'another world, another dollar', and it is known from historical recordings that he gave a short, but moving sermon, and then demanded the recorders be turned off before dying. Some say he vanished into a cloud of dust when he died, and thus ascended directly to Heaven in his body. Others dispute this as fanciful myth-making. In any case, representatives of the Appleseed Order command a great deal of respect even among skeptics in the Outworlds.
Most of the time, these robot packages sent by the Appleseeds failed.
But of the several hundred times they tried, they succeeded at least two dozen times. And thus, when humans went into space, they found two dozen worlds where all they had to do was plant a seed, and it would grow.
A hundred years later, and half of the human race is in space. Half of those in space live in the Sol System in the Luna Domes, or in the Beltholes, or under the ice of Titan. The other half, a full quarter of humanity, are scattered over two dozen worlds that range from ten lightyears from home at Nearlyhome all the way to a thousand lights out at Darkfall.
Earth, after its long effort at birthing children, has turned inward, and is turning strange with cybernetics, and broad-bandwidth communication links, and new forms of art. The Outworlds are not provincial, in that they do come up with their own ideas, but they are isolated from Earth, and to a lesser,but still large degree, from each other. And they mostly like it that way.
In a few hundred years, after the planets are subdued, may come the time of competing interstellar empires, but for now there is little contact between the many planets.
MORE LATER...I was going to type up a bunch of seedlings, or a few anyways, but I'm tired.
1.