I'm trying to figure out how to build my virtual economy. It seems like some games have one currency and some of them have up to 3 and 4 different ones.

The game is an action game which is currently single player but I'm planning on adding a tournament mode that allows users to compete against each other. The virtual goods that a user would be able to purchase would be either customization to the character or powerups and utilities that give the character more abilities in the game. The character is able to gain coins during game play.

The advice I'm trying to get is whether or not it makes sense to set up more than one currency and more than two currencies? What are the pros and cons? Reference to some resources that indicate research would be great.