World of Warcraft should automatically update itself when there are patches available. There is no way around it. You must be playing the most recent release or you don't get to play.
Sometimes when you click on WoW, and log into your account it says new patch, and it loads to 100% then turns off WoW and opens a mini tab that shows the patch being downloaded.
just delete that patch in your wow client folder
This answer is better answered by Blizzard Tech Support. Try going to the official forums and asking there. You will need an account to post, but if you are already playing wow, you have an account.
Worgens and Goblins will not be available until you actually have a Cataclysm account and Cataclysm is active on the servers. This will be December 7, 2010.
A patch mirror in WoW is a common element for that whenever a new patch is released for the game, it can be downloaded from different sources. One popular place for the patch is DepositFiles.
I do not know for operating systems. If you go onto your wow account though online at worldofwarcraft.com, if you have already verified you bought the game, you can download it on worldofwarcraft.com. However you still need to have acces to an account and to game time.
No, you will have the same download speeds. It all depends on the quality of the server(s) you're downloading from.
Cataclysm Patch.
Start your WoW game like normal and Blizzard downloader should automatically start downloading the Latest patch.
You can just delete the patch file once downloaded and installed by wow. You can not revert wow to a previous version because wow is auto-updating. Every client has the exact same version (for their OS).
no
Use the wow-launcher? It auto-patches the game and it starts automatically.