This link has lots of good info.
Generally you want to have ~20 buy-ins for your stakes in NL. However, until you can have some degree of certainty that you are a winning player you are not really managing a bankroll. Winners have bankrolls, losers have "the cost of learning," or "entertainment expenses."
If you can add to your poker accounts from other sources, your "effective bankroll" is more than what you have on the accounts. So you may have 20 buy-ins for NL10(or NL25 or NL50), just not all on the poker sites. Also just because your are rolled for a game, doesn't mean you should play it. Having recently made the switch from limit to NL, I'm rolled for a game much higher than I'm playing, but I am starting where I can learn the game while risking less.