Somewhere in the a-b-c range. The question of when will depend on a number of variables that you can only answer depending on the specific situation. More imp

Somewhere in the a-b-c range. The question of when will depend on a number of variables that you can only answer depending on the specific situation. More importantly, ask yourself how much risk will the potential co-founder be taking on? In stages a-b-c there's plenty of risk; after f; there's not so much. If your potential co-founder is unwilling or unable to assume a significant amount of risk, relative to yours, then they're more of an employee than a co-founder. Something you'll discover is that there are plenty of people who want the "co-founder" title but aren't willing to assume a commensurate amount of risk. They'll tell you to go out and get the money, then they'll jump in once you've guaranteed their paycheck. Avoid these people.