Question Architecture: storing + streaming a procedural/open world

Hi I'm hoping that someone can give me some pointers on open world architecture. Like, general ideas on how to store world data and load it into unity when the camera goes to that area. Also maybe details on handling floating coordinate systems?

Background: I'm new to unity, and starting with dots. I'd like to prototype an open world builder game focusing on procedural asset placement. okay to use prefabs, but want to procedurally place terrain and objects during a "level gen" phase of the game, then stream that to the camera as needed.