Tools, languages, libraries and API's for development of a MacOS wide application Please just assume that the user has accepted whatever permission are required. 


Is it possible to listen to window actions under MacOS? In Swift
preferably? 

For instance, if a window moves, is resized, minimized and etc. 

Preferably without polling and comparing states.
Is it possible in Swift language get info on windows, or manipulate windows of other applications? Or do you have to rely on using something like the dreadful AppleScript? 
How well does Swift stand on its own when developing MacOS applications? What fallbacks are required? 
Is LUA and hammerspoon perhaps better suited for this kind of task? 
Is it possible to draw around windows to add buttons and what not under MacOS? Would this be possible in Swift, AppleScript or Objective C?
No, there is no public API for these events on macOS. The programming language does not matter.
Yes. Using the Accessibility frameworks. The programming language does not matter.
Swift is Apple's recommended development language for macOS. Discussions about Swift are better answered elsewhere.
See above.
Within your own application, yes this is possible. Sections of windows can be transparent. This is possible in Objective-C or Swift but not in AppleScript. See xScope as an example of display wide overlays.