5/ Reverse geocoding may seems simple, but there are lots of things to consider.
First up, different parts of world are structured very differently, with different admin hierarchies and ways to show addresses.
We format the address as expected locally.
BTW - the templates we use to do it are open sourced: https://github.com/OpenCageData/address-formatting Pull requests gladly received!
6/ Of course most of the world has no hierarchy as all, it's water. We handle that as well.
See our thread on geocoding the oceans: https://en.osm.town/@opencage/110207789147450417