Revenue comes from selling something. What you sell can be products, premium subscriptions, or sell your members as advertising views. There are hybrids too: joint partnerships, offline integrations, etc.
That's why you need to crunch the numbers... If 1% of people upgrade what does that mean? ... 2%? 5%?
But before you even go there size up the market. If you're going to attract 5000 users total, even 10% isn't much.
If you can't reconcile that, find a new opportunity.