If you can’t build your version 1 with three people, then 1. you need different people, or 2. you need to slim down your version 1. Now, before I get yelled at, this doesn’t apply to every project, but I do believe it applies to the majority. And sure, if you are building a weapons system, a nuclear control plant, a banking system for millions of customers, or some other life/finance-critical system, then you may need a fourth.
But keep it in mind: three for version 1. Remember, it’s better to make version 1 half a product than a half-assed product. Three people will keep you closer to half a product and a cleaner, tighter, simpler base on which you can grow later.