You do not need the Redbox. The Redbox is just a starter and is a cheap way to get started. It comes with the following and only cost 20 bucks.
- 32-page book for players, with rules for character creation and a solo adventure
- 64-page book for Dungeon Masters, with the rules of the game, advice on how to run the game, and adventure content
- 2 sheets of die-cut tokens for characters and monsters
- Cardstock character sheets and power cards
- Double-sided dungeon map
- 6 polyhedral dice
It'[s just a cheap way to try out the game. You can totally play by just buying Heroes of the Fallen Lands, Rules Compendium and don't forget the DM's kit.