It's useless to bet on any number, as it's depend on how active are you refs, where they come from, what activity they perform ect... If all your refs just click the ads for exemple, you will need a very very large downline.
Since as a premium member you earn a 10% commission from the offers, surveys and tasks; you would need the total of your refs earn a 3000$ per month. As said if they just click the ads for $0.03 you can do the math, the same as if for exemple you earn $0.50 daily per ref
Maybe not an usefull answer, but it's quite difficult without knowing who will be your refs