No you do not.
Guitar Hero World Tour is Guitar Hero 4.
yup
No
NO
I believe you can, yes.
Guitar Hero World Tour and Guitar Hero Metallica
Yes, many people around the world play Guitar Hero. It has an international following.
Yes, the controllers can be used for all guitar hero games
yes
no, each game has a different song except for guitar hero smash hits
Yes. You can play any guitar hero game (including Band Hero) with any guitar (including the Guitar Hero World tour guitar.) As long as the game and the instrument are for the same video game console.
You can play Rock band with a guitar hero guitar, but you can't play Guitar Hero with a Rock Band guitar.