I fear this may be a result of my current lack of documentation but all of what you have just mentioned is already possible.
I do admit that currently it isn't really accessible by the general user.
The reason why the default style uses the same elements for every window is because it is the most basic style, the default. But you are not limited to this style, close to everything is customizable from your end if you go look for it inside the AppData folder. (Despite the file extensions you can open all of them with notepad++)
I see potential for an in-app editor of sorts so I'll add that to the production list.
I'll also start working on documentation so that users can get a guide on how to create their own layouts and elements.