Start with a monolith for your core business logic. Rely on external services for things outside your value prop, be it persistent storage or email or something

Start with a monolith for your core business logic. Rely on external services for things outside your value prop, be it persistent storage or email or something else. Keep on building and growing until the monolith is causing teams to regularly step on each other's toes. By that I mean, continue well past teams needing to coordinate or needing dedicated headcount to handle coordination to the point where coordination is impossible. When that point approaches, allow new functionality to be built in microservices and gradually break off pieces of the monolith when necessary.