Howdy, and welcome to PhotoStructure, @tranquilian!
We’re not quite (ok, not close) to feature parity with Google Photos, but I’m working on it every day.
The directory hierarchy is completely customizable through advanced settings. More details are in this post.
Your PhotoStructure library has a SQLite database, and a bunch of other supporting files:
PhotoStructure reads and copies Google Takeout JSON sidecars. More details are here:
PhotoStructure does create optimized preview images for browsing, but keeps your original images and sidecars completely intact.
A bunch of metadata editing features are on my to-do list as soon as user authentication is complete (which is the next feature I’m going to ship), so this is Coming Soon.
I think this will be a good feature to add! Be sure to vote for it here.
Note that it will be opt-in, and built after I add captured-at editing (which you should also vote for).