It depends on your goals and situation. Are you willing and able to deposit again? Then the money only need to last until your next paycheck maybe, so make a budget. If you want to play 5 events per week, you can buy in for 2-3$. If you cash in some, you can deposit less or not at all next month. Otherwise deposit another 50$ on next paycheck.
Or are you determined, that this is going to be your bankroll, you think you are a wining player, and it should grow from here? Then follow the advice of 100 times the buyin. There are not many 0,5$ events though, so look to play some 0,25$ multi table SnGs. If it go well, start to mix in some 1$ multi table SnGs.
The multi table SnGs are nice, because they are raked lower. For the 0,25$
pokerstars keep 8% of the buyin, for 1$ its 9%, but if you play tournaments its 11%. These differences might seem small, but they matter in the long run.