Do you have beta customers? If so, why are they using your product? What are the key benefits, why they prefer your solution over others? What’s the value you provide to your customers that makes your product superior to existing solutions?
Story telling is a very powerful way of getting a message across. I would start by convincing first why you’re doing your product (why there’s a need for it) and then explaining how it’s better than others (the value).
Next, if you can explain that there’s a big enough market for the product and it’s achievable (e.g. Peter Thiel have some excellent points in his book Zero to One about tackling the smallest possible market first and becoming the dominant player).
Then you still need to convince that it’s your team that can pull this off. And naturally you have to share your execution plan how you’re going to do this in practise.
If you can convince your audience that you can make this to happen and you know what you’re doing (+ they buy your plan) the actual numbers are less important at this point. No one can expect you to come up with exact ways or data when you’re not at that point yet.
Still, you need to have your facts, projections, guestimates and data to back you up but they are just that. Support material at this point. The main task is to sell your overall story and why it’s relevant.
Most of the decisions are made by emotions (hence the story-telling), and facts are there to rationalise the decision. Good stories sell, especially when the business case underneath is brilliant and solid.