Young poker players and their winnings?

[Newt_Buggs]

I just thought that I'de double check and see if anyone had some insights that I'm missing. I'm extreemly fortunate to be a young successful profesional poker player. I did some basic research on how to invest my winnings and decided on the Vanguard 500 Index Fund. I read good things about it and once I got past $100K invested they bumped it up to admiral shares lowering the fees.

Some questions:
-Would it be a good idea to diversify outside of just a single fund? How important is this?
-Are there any investments that have a higher average return that I might be missing? I am completely risk neutral and don't mind large fluctuations as long as I am receiving a higher expected rate of return as a result.

Also please note that my time is limited because I am still in school and am looking for investments that don't require a significant amount of time.