Ask HN: How to write a convincing financial projection with little evidence?

I'm the co-founder of an early-stage startup and we plan to raise our seed round at the beginning of next year. I'm currently struggling with the classic 3-5 year business case/financial projection which includes numbers like earnings, growth, costs, cash flow. Obviously, investors want to know how fast and how big a startup can grow, but at this stage, it feels hard to come up with convincing numbers. - How should we project our growth rate? The idea was to take our existing sales pipeline and anticipate a realistic closing rate of e.g. 30%. But what would be the growth rate for the following years? Should we look at the industry average? - Does it even make sense to do a 5-year projection? would a 1-year projection satisfy seed investors too? Any advice is highly appreciated!