with how much money is profitable to start playing in nl2 and nl5
It is not profitable to play 2 and 5 NLHE, because we don't want/need to play millions of hands in these primary stakes.
It is not profitable because the ammount invested is so little, the risk is so little, thus the profits could not be the opposite, the profits are very little as well.
So, when we do play 2 and 5 NLHE we are looking for a "hot streak", some particular sessions where our winrates booms and we make preposterous ammounts of profit, then our first plan is to move up immediately to 10 NLHE, where we can be wondering a little about being profitable, depending on the country you live and the respectives taxes laws.
We are aiming to be luck at those primery limits, so as other have said, we would recommend something that varies from 20 buy-ins to even 100 buy-ins, it all depends on your overall game plan and your own style of bankroll management, if more passive or aggressive.
Even if you are a very good and experienced player you cannot avoid huge downswings at those limits, because absoltutely anything can happen when you are playing with less skilled players, that are just looking down at their hole cards and playing "faced up", almost everytime, but sometimes they surprise us because they are not machines.
Regards;
Carlos 'Aballinamion' Barbosa