I couldn't say for sure, but if you are having problems with badly behaved bots wasting your bandwidth then I guess it's worth a shot.
Yes. Just create a file called .htaccess with the required content and place it in your domains web directory (by default this will be named the same as your domain).
Note: .htaccess is a 'hidden' file, as such it will not show up in your FTP client unless the client is configured to show such files.
Nope, it is up to you to create and maintain the .htaccess files for your domains.
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