My suggestion would be that you approach a professional in the field (for instance a friendly VC contact) and give them the figures as much as you can and then work out a reasonable bandwidth together.
This will take you some effort, but at the end of that you will know a lot more about your company than you do now.
Make sure that you do not end up paying Mr. X his own investment back as a salary, otherwise he's just an equity-for-work employee, not an investor per-se.
If I were you, I'd be going about it the opposite way: put together a good, detailed business plan, and figure out your most effective growth path. Then, decide how much (if any) outside capital is required to finance that plan. Then, try to find what is the best way to raise the needed cash, and how little equity you'll need to give up in order to get it.
@jacquesm Average sale varies from 1k per month to 15.Time:8 months. The potential market is in the trillions. "Make sure that you do not end up paying Mr. X his own investment back as a salary, otherwise he's just an equity-for-work employee, not an investor per-se." -Good point.
@michael_dorfman True. The issue is that Mr.X is willing to work on the project for one year without any cash compensation.