This is awesome! You should add ctrl+[ as an alias for escape as vim does. I've used that for a while now, and actually reaching up for escape feels unnatural now.
inoremap kj <ESC>
In GNOME: System → Preferences → Keyboard; Layouts; Options; Miscellaneous compatibility options → "Both Shift-Keys together toggle Caps Lock" (You can also remap Caps Lock in this same dialog, so the change isn't just for Vim. It's under "Caps Lock key behavior". Also, having a compose key is awesome.)