CA Qualified (NZICA) and have done something similar in the pass (mobile apps and you can view the sample on my linkedin page), currently engaged to do similar line of work (new ventures) for a company up in Papua New Guinea.
My approach:
1. Understand your product offering, target market, competitors, business environment and overall business strategy / positioning. Effectively the scoping.
2. Understand what are your setup costs (capex and capability requirement), delivery of these capabilities, etc.
3. Understand what are your recurring revenue streams, opportunity, weaknesses, strengths and threats. Follow by how to turn these into your advantage.
4. What assumptions and drivers are needed
5. Construct financial model
6. Sensitivity analysis
7. Presents