two things,
launch options with the launcher dont work. you need to add:
-game "C:\Program Files(x86)\Steam\steamapps\sourcemods\gesource" -console
to Source SDK Base 2007 in steam launch options
change the directory to your local install of gesource / steam.
then the console should appear, next type:
default is
As for binding the console to a key, make sure to choose one that is not different in other nations kayboard layouts. For me it worked when i bound to F9.
An alternative to Deaths method:
find the config.cfg located in ..Steam/Steamapps/Sourcemods/gesource/gfc/
Open it with a Text editor and add the line:
bind "F9" "toggleconsole"
Save the file, start GES and press F9 once the main menue is loaded.