Emacs: Custom keyboard layout - language environment - is this or can this be independent from the OS or not?

Question

I start with my intended result, so maybe it becomes apparent, why I have my difficulties to find a useful answer on my own at this moment.

I want to use a slightly modified keyboard layout of the Space Cadet Keyboard (adjusted to a German layout and some minor changes) with proper keybindings for the alternative characters (math, logic, greek letters ...).

The section about the language environment setting of the Emacs Manual indicates the dependence from the OS settings. Therefore I guess, it would be possible to define a custom keyboard layout system wide and tell Emacs to use it, possibly by selecting the proper input method?

Changing the key bindings is only supposed to bind commands to key combinations, right?

Probably, my question is rather stupid. I think, I would like to just use a modification within Emacs, imagining that I could bind the output of utf-8 characters to such combinations.

But is this a silly approach and should I just care for defining a keyboard layout for the os (Linux) via xkb?