Interesting read and I agree with almost all of it. Great pointers.

The one comment I would have is on "plots". Many players aren't self-motivated enough to come up with goals for their characters that might create their own "plots". If the players ARE motivated enough and do create a character goal and "plot" then without any structure whatever goals they come up with likely conflict with the goals of other characters which generally leads to problems in and of itself.

One character is looking for vengeance. One character wants to end slavery. One character wants to become the supreme leader of all space. One character wants enough loot to buy a planet and retire. One character wants to lead a mercenary company, fly around the galaxy causing chaos and destruction just because.

Nope. Character created "plots" based on player developed goals for their characters often don't work though if the characters are created with a common backstory and interests then they might come up with something, usually it doesn't work like that.

In my experience, a sandbox needs to provide "plot" seeds. Significant events, significant NPCs, significant interactions that can draw and hold the player attention and motivate the characters to become involved. Put a few of these "plotlines" into the sandbox with events progressing slowly but independent of the characters then give the characters enough information about what is going on that they can choose what to do. The difference between this and rumors is that several collections of rumors are connected behind the scenes to independent series of events and this can then lead to the larger ongoing story elements in the background where the characters can choose to become involved or not.

So basically, every story has plots, every world has plot lines, a world is not just a collection of independent random events. Players/characters obtain information through interactions with the world but the DM is guiding those interactions and needs to feed information allowing the players to become more aware of some of the story currents in the world so that the characters can choose to dive in or make their own currents.

Just something to think about - to me, a world always needs plot lines since there are always things happening ..

e.g. a specific faction trying to dominate the drug trade between worlds, introducing a new, highly addictive chemical that they can both sell for high prices and use to create indentured slaves. The characters could encounter folks begging on street corners, people wearing collars declaring their status, looking sickly. Dealers selling the big new thing - "try a bit, I guarantee you'll like it".The characters might decide to get involved and they might not. These encounters lead to a star spanning cartel with political influence trying to bend the social fabric in their favor, convincing the government to declare that indentured servitude is legal since they are saving these folks from their addictions and giving them productive work.

This could be one of half a dozen plot lines moving forward at local, planetary and inter-stellar scale.

The world needs more than the factions, it needs the effects of what these factions are doing that could pull the characters into their plot lines. But, it is challenging to manage well without giving the players too much or too little information.

-------------------

P.S. I don't really understand the player reactions in anger to the player with the space ship asking for a fee at the beginning or the reaction of that player saying "just throw my character in the brig". That should have been a great role playing opportunity to let the players establish their characters but instead it sounds like it went sideways for real life personality reasons. To be honest, for me, that would have been a first red flag that there might be an issue of some sort.