How do you define different stages of a startup? And what are key roles of founders at each stage?

I would split it like this: At the beginning there are only founder. Founder somehow found a vision of a cool product. At this point founder has two most important tasks - main one is to check his vision in the reality and hopefully confirm it. Another important task is to find and inspire his core team (might be a co-founder might be not). On the next stage the goal is similar - check the idea and try to approach product-market-fit. The best check is payments, so founder have to find-and-sale. Founder as bearer of the vision is the best salesman, so founder just have to sale. When we confirm the idea by first payments we are at the development stage. Tech founder write code, non-tech founder prepare a marketing. When ready release a product start a marketing and look how it’s going. Iterate. At some point you should have enough cash in the bank (MMR) to hire someone. I would hire support & customer success first, because it’s time consuming and then dev team to iterate faster. Founders start to be a managers and continue to do rest of the work + drive experiments to growth. At some point MMR should be enough to delegate most of operations and focus on the company development and growth. But I’ve never been there)