Is there a keymap I can add this to which will also cover editing in
minibuffers, so I can use my weird input method in isearch and that sort
of thing as well?
Caveat: I'm not following this thread.
In general, you can bind keys in the minibuffer
keymaps. The most basic is `minibuffer-local-map'.
See the Elisp manual, nodes `Text from Minibuffer'
and `Completion Commands':
https://www.gnu.org/software/emacs/manual/html_node/elisp/Text-from-Minibuffer.html
https://www.gnu.org/software/emacs/manual/html_node/elisp/Completion-Commands.html