It is possible to use certain joysticks with WoW, although it does not support it officially (requires some fiddling and some programs). The only hardware they support for input and control is a mouse and keyboard.
The link below to the official World of Warcraft forums might provide some help.
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You mean like a joystick or a gamepad like Xbox or something has? no.
Yes, you use your Battle.net account to log into World of Warcraft.
I'm assuming you mean "How many Gigabytes does World of Warcraft use or take up?" The answer is approximately 17.5GB. That is the size of my file atleast.
Yes you can use a joystick on the PC. When you start Fallout New Vegas with a joystick connected (or connect when game running) it will recognize the joystick and use it as the only input device (yeah, the game designers made it so the keyboard/ mouse is disabled, which sucks).
Buy a game card or use a credit card