- Yes you can check the object location via the use of a modal operator
- Yes there is an update callback functionality for properties that can be called every time a prop changes
- I am not so sure about that one, you will have to look at the API ref docs.
I wish I could help you with the internal code, but Blender source is a labyrinth without a map and being 2 million lines of code makes it very challenging and slow to learn how it works. But its high modular and Blender uses a ton of internal functions to do even the most basic functionality so everything is possible even if you don’t intend to change the source code itself but extend it.