** How do I start Emacs as a GUI application from the command line?

Replace the binary `/usr/local/bin/emacs' (or wherever you installed
it) with a file containing the following two lines (of course you need
to change the pathname according to where you have put the Emacs.app
application bundle).

#!/bin/sh
/Applications/Emacs.app/Contents/MacOS/Emacs "$@"

Then typing `emacs' (provided /usr/local/bin is include in your PATH
environment variable) will start Emacs in GUI mode. Typing `emacs
-nw' will start Emacs in terminal mode.