You will not go broke due to variance, but unless you already know, you are a winning player, its not really possible to have a bankroll. If your ROI is negative 20%, then 750$ will on average be gone after playing 1.700 2,2$ MTTs or 3.400 1,1$ MTTs. Just saying this because a lot of people, who ask these bankroll questions, dont actually know, if they are winning or losing players. That being said with so many bullets in the gun it is also possible to improve your winrate and turn from losing to winning player, before the money in gone.