My recommendation would be to bind `C-x C-k` to `kill-this-buffer` and unbind `C-x k`, or bind `C-x C-o` to a hydra that lets you repeat `C-o` i.e. hold down ctrl and repeat `o`, to cycle windows. Or both.

Alternate, try out `ace-window`.

I'm not sure about "too easy to confuse for a newbie." These kind of mistakes only happen when you are switching buffers rapidly without checking prompts, and newbies won't be doing that. And the default mnemonics are (unlike much of Emacs) good for these tasks. So rebinding doesn't feel like a big ask.

(Agreed `C-x b` should be removed imo.)