Is there a single shortcut to start inserting in the new line at end of the file?
I\'m aware of G + o combo.
Adding the following into ~/.vimrc will create one for you:
:nmap ^A Go
To type the "^A" first press Ctrl-V, then press Ctrl-A. You can then use Ctrl-A to append at the end of the file when not in insert or visual mode.