Long story short, at least about half of what you expect to make, including the original capital. If you're very lucky, then you'll make 3 times as much. If not, 50% gain is more than what people usually can ask for. Incoherent rambling it might seem like, this is a nice general rule to have.
For example, if you expect to pay 1 coin to make 2 coins, it is better to save up 1.5 coin. That 0.5 coin as a backup will help you if you run into problems. Usually problems that would prevent you from breaking even. You cannot go into business with exactly the amount of money that people told you you would need. Most of the time, any additional fees would cause unnecessary stress and effort that could go into making more money.
This goes for Steemit as well. It is the wild west but unlike the oldies days, those who learned faster will earn faster. You need to understand new concepts earlier than everyone else and know how to use it. Time is still the advantage, those who understand the technology better will be able to exploit it to their benefits until mass adaptation diminishes the returns. Once you understand the way it works, then you would need capital.
Key point being understanding how it works first, then start putting money into it.