Going to talk world-building, and I’m going to do it with a little help from Croidure, who’s been running games in a homebrew world for a decade or more. Croidure’s take on world-building is a little different than mine; I’m more of a ‘throw it at the wall until it sticks’ world-builder, she’s a little more methodical. But both methods work; we both aim for the same thing; a consistent, living world with its own quirks and rules.
I’m going to start with the old author’s saw; be willing to kill your darlings. If something doesn’t fit with the system you’re using, toss it. If something doesn’t fit with the narrative, shelve it. If you love it? Kill it as many times as you have to.