The 300 BB figure is for limit, not NL. So is the Microlimit forum, where you asked another NL question.
Here is a
past post I made on bankroll requirements for NL in the Beginner's forum. Please note that you should establish that you are a winning player before worrying about a bankroll. If you have not established that you are a winning player (as your other questions indicate), you need a budget, not a bankroll.