Seriously, get something real, prove you're on to something, and THEN talk numbers with investors. You've got a bigtime uphill battle without at least one solid proof point. Get that, and then hockeystick that sucker up!
I agree with you - we won't be raising money till after we launch and (hopefully) gain some traction. But one of our founders is handling the business side of things and really wants to get at least some rough numbers now. Given his considerable business experience (and the lack of downside to letting him create his model), it sounds like a reasonable request. Rather than have him pull the numbers out of his head, I thought it would be better to do some research.
Don't worry, all our technical people (myself included) are completely focused on making the product as great as possible for launch! And, for what it's worth, we are following a very quick schedule - just two or three months of part time development before we launch and start iterating on user feedback.
It's nice rhetoric to proclaim that since user adoption figures cannot be predicted with accuracy, they should not be predicted at all. Even without accurate forecasts, it is trivial to calculate the required breakeven users and examine scenarios where that breakeven is achieved in a short,medium, or long ramp period. Other valuable metrics are also more easily discerned from a model than by pure guess.
It sounds like me that that business guy is simply doing his job - and it sounds like he knows his job better than many readers here.
Warning signs! Translation: "He doesn't know what he's doing" (or he wouldn't be making predictions on made-up numbers), "and I'm letting him waste some time" (ie, "the lack of downside").
Not sounding good :)
The portion of your post that indicated that potential investors were interested in the numbers threw a red flag up for me.
I'm willing to defer to the business-founder with experience on this matter.