The great civilisations are still very much in their growth phase - while their exact numbers are generally not disclosed to avoid the other sides getting an advantage, even the largest measure their expanse in dozens of planets, not hundreds much less thousands. It means while specialisms exist, it is very rare for there to be worlds devoted to a single purpose or industry.
Solar systems are split between fully developed “core” systems, up and coming developing systems and small colonies and outposts where the primary goal is survival while they get on with whatever business encouraged them to go there in the first place and nobody has any intentions of living there long term.
How each system develops depends very much on the system and the civilisation - being traditionalists the Earth Empire are very fond of planets, perhaps to separate themselves, the Federation love their orbital megastructures, the Co-op meanwhile, lacking the resources of the other 2 human civilisations will often as not be on asteroid colonies.
Either way, there are some basic rules for empire expansion, governed by some simple precepts:
This means that establishing a colony in a new system is a big effort and tends to follow the same basic paths:
Phase one is your resource extraction and heavy manufacturing industry to build everything else. Raw materials and construction equipment are big and bulky, making them very expensive to ship in. Initial development will focus around the most convenient resource-extraction site - ideally a planet or moon with low gravity or asteroid mining. Your settlers are living in pre-fabs and better like the taste of freeze-dried space rations.
Phase two is food and water for the organic races, both are also bulky and heavy, especially as you need a continual supply of them. They are however relatively easy to get producing in system, having a planet with an agreeable biome for farming helps keep your costs down and food diversity up, but failing that orbital hydroponics gardens are a tried and tested technology.
Phase three: Now you can feed people and build stuff you start the process of actually doing whatever you bothered colonising the system for in the first place. What happens varies by civilisation and by intended use of the system - for general colonising you start looking to move people in and building the infrastructure required for them to actually live there. If on the other hand the system isn’t overly suited to life and you are only here for the resources it will focus on manufacturing facilities: it is almost always more economical to refine and manufacture in system and ship out the finished products.
Either way until you have finished phase three the colony is still a burden on the parent civilisation - the colonists want things: supplies, luxuries, news, but they are not producing anything to export, which means less reason for traders to go there. Broadly the government needs to compensate some traders to make a low profit outbound run carrying mostly food and essential supplies, and a practically empty return trip. Once you complete phase 3 the system is a well established small colony and economics starts to sort itself out naturally.
Phase 4, which depending on where it is and what the political climate is like, may be phase 0.5, 1.5, or 2.5 is where you drop a load of defenses in the system such that it stays yours.
This brings up governance: much like the frontier towns of the US or the British Empire of old, a star system has to be mostly autonomous. In the best case it takes days to get something from the rest of the civilisation, be that a communication, emergency resource, skilled person or military aid, and that’s if what you want can be found in the nearby colonies, a conference call with a centralised government can take weeks round-trip time. This means balancing autonomy of the colony and the colony government against loyalty and reliance on the parent civilisation.
The overall method of civilisation government needs to cope with the time lags and relatively sparse communication between its constituent parts. The Earth Empires solution was to resurrect the feudal model of old earth, the Many’s solution, well, let’s just say that Mega Democracy is interesting.
These are colonies that have come up in play, often as backstories.
Helion II is a medium sized desert/arid planet in the outer rim of Federation spaaaaaace. It orbits the red giant star Helion which is in the early portion of its red giant phase.
Helion II's claim to fame was as a former Federation convict world, and was used for the dumping of low risk convicts from several Federation Prisons to help deal with overcrowding (the biome is human survivable, but not exactly optimal, so people weren't exactly queuing up to settle voluntarily). Over the course of years the planet's unfortunate inhabitants set up a loose community of farmers and ranchers that has since resulted in the planet's declassification as a convict planet. The official designation is now Outer-Rim Agricultural World, but it is colloquially known as Space Australia due the historical similarities found with the nation of the same name from Earth's antiquity.
The inhabitants of Helion II are tough, resourceful, and have a very straightforward way of dealing with life on such a dry and arid planet. Violence, while not widespread, is often seen as a good way to deal with any perceived hostility. Is is recommended at anyone planning on visiting Helion II avoid direct eye contact with the native population.