Great article, many thanks for posting.
3 comments though...
1) Many admins can't afford a secondary backup server, however many dedicated hosts provide a free FTP backup server - it might be worth adding some details of performing an FTP copy of the backup.
2) Rather than shutting down the webserver it is possible to gracefully close vBulletin, have a look at this:
https://vborg.vbsupport.ru/showthread.php?t=254529
3) It is also probably worth detailing how to setup the backup script as a cron job