All you need to do is go to your hotkeys.rc folder and add a hotkey that does the command !Hideall. For instance mine is Ctrl W. Whenever i load up a game i hit that and everything hides, you will also need a hotkey for !Showall which is used to bring your start menu back when your done playing. If you need help on making hotkeys look at your hotkeys.rc file and there should be a few examples in there about how to hotkey Bang commands.