all great ideas... and some good show/story i wasn't even thinking about.
some crazy ideas I have right now is a sphere (or sector we don't know for sure how they are doing 5e yet) that is a star/sun, and 3 planets... 2 gas giants and a waterworld.
1 gas giant is mostly a hallucinogenic gas, the other is smog/debris because it was once a livable world blown up and held together, somehow. around the hallucinogenic gas giant are 3 small asteroid 'city' size orbiters (too small to call moons) that hold 'miners' that dive in and collect the gas. this gas is both a drug, and a drug. As much as anyone can pop some and have a 'trip' if mixed and adjusted right it can be a helpful medicine too.
so there are traders for medicien...and black market runners for the drugs (and sometimes the same person is both)
the waterworld has a full size moon (smaller then ours but big enough to have a dozen cities and a small village or two... but nothing can grow on it (nope not even with druid magic). The water world itself is ruled by a coven/collective of Abeoliths that have dominated super kraken and have underwater races in there thrall... so far they can't leave there planet, but if they do oh boy would they be a threat... the problem is that deep under that sea the world itself, the ground is SUPER rich in minierals... diamonds, platinum, adamantine, mithril... more mystic metals (I have my own homebrew ones)
the king of the main kingdom of the moon cities is a powerful Psychic. He comes from a line of powerful psychics. He himself is a half elf, but if you go back 3 generations they were human... they married into elven lines when they were trying to expand but the elven family fell instead...but it does make the king more long lived. He though knows a BIG universal secret... or at least he thinks he does since he is a Great Old One pact Warlock (that is the psychic part) and he thinks his patron is the star dust itself... but no it's the hive/coloney/collective of Abeoliths on the planet below... they secretly control him through con jobs.
there is a small resistance to the abeoliths... and it comes in the form of the all mighty mechs. a group of warforged and auto gnomes that live inside the moon in caves and are trying to stop teh abeoliths from advancing... but the king calls them clockwork terrorists.