Also the Alt key + letter keys produces a series of key codes prefixed by escape, so one can use any single letter normal-mode command with the Alt key, resulting in "Escape"+<key>. This is convenient to quickly switch to e.g. moving the cursor with e.g. `Alt+j` to both escape from insert mode back to normal mode _and_ move down a line.
I knew about the Ctrl+[ but this might be a game changer... I have tried vim several times but have never gotten used to the idea of staying in one mode or another (emacs chords is more intuitive to me). This seems promising.