I have a moderate to large-sized game: the entire world will likely end up around 0.5km/0.5km relative size, most of which will consist of an urban setting: criss-crossing streets and buildings with complete or semi-complete interiors. I’ve been pouring over World Composition User Guide | Unreal Engine Documentation , but most of that seems to assume the main intent is to stitch landscapes together, and I’m super-confused about my own use-case: should I be setting up world composition and breaking the game into big chunks, or should I eschew that in favor of streaming volumes, and break it into lots and lots of little chunks?
That’s an easy fix then, thank you! 
This is only moderately related, but do you happen to know how to pull off long horizontal views with level streaming, like long streets that let you see across 4-5 discrete streamed areas? The best idea I’ve had to handle it is to make each level a small island of detail and lots of low-poly mockups of surrounding levels, so the higher detail versions get overlaid over the lower-poly as you get closer.
You should use regular level streaming. It will work well for the case you have described (that’s basically what it was designed for). World composition is most useful for really huge maps, which (if you are on a planet like Earth) are likely going to be mostly outdoor environments.