A realistic business model.
If you are at all handy with excel, then you can probably run up a business model. We budget between 4 hours to 4 days to develop and vett a business model. There are 2 important aspects to every business model:
1. The dynamics.
The dynamics define the shape of your business. It defines the number and interplay of the key business levers: number of users, number of uses, distribution channels, pricing, costs, etc. If you have a transactional model, an ad model, a subscription model, a hybrid - these will all be drawn out here. Very sophisticated models can be built with hundreds of levers and very complex formulas, but they aren't really what you need for planning and projection of most new products. What you need is a sense of how you expect to acquire users, how you expect to generate revenue, and the various factors that affect those numbers.
2. The assumptions.
This part can be tricky. Most people are motivated to show that their product or project will generate xx million dollars by the end of year 3. Sometimes this is to get project approval from higher ups, or to get funding. Equally often, its because the people who build the model are such great champions of the product that they are very optimistic in their assumptions. And that optimism can be subtle, and even little bits of optimism can change results dramatically.
So - the best thing to do is to have 2 models. The optimistic and the realistic (it will seem pessimistic, but its always better to have the chance to over-deliver)
We'll run you both scenarios. The aspirational, and the one you need to be prepared for, just in case user acquisition is harder than you hope.