I have a slightly different opinion. Start with a mostly monolith, sure, that makes sense. But also start off with just one separate microservice for something

I have a slightly different opinion. Start with a mostly monolith, sure, that makes sense. But also start off with just one separate microservice for something important. It's important that you establish good patterns for integrating services in to your codebase early on. Its really easy to write a monolith without any thought of external service abstraction, which makes it WAY harder to do down the road if you decide you need to.