The longer I do this, the more I realize that the way a recent immigrant standing behind a pushcart views things is the right way to view things. Also, I noticed when I used to sit in a board meeting with him, that this is the way Alan Patricoff views things, and he has done pretty well.
You are not opening a business that sells a product or service for which there is a preexisting market, nor are you entering a market in which there are other easily ascertainable metrics, so you cannot expect to have meaningful assumptions, much less projections in the very early stages. Therefore, I would not try to sell these to prospective investors. Basically, what you can sell is the size of the market as you define it, the idea, the team, and the team’s ability to execute on the idea, or on a different idea to which you pivot once you learn more. Anyone who does not want to invest on this basis, should not invest in you. They will only become disappointed and possibly angry later. The best possible investor is the one who really understands what you are doing, will help you do it as much as they can with the money, and otherwise.