Is it necessary for you to have played The Witcher 1 and 2 before 3?
It's not mandatory, but it will help you understand the game. Go to the library and read some books if you can't afford the game. If you're a fan of the game, you should definitely play the first and second games. There is a lot of time before Witcher 3. There was a report on Jun 14, 2013.