Thanks, really appreciate the pros and cons here. To be clear, and I understand the confusion: I'm actually building more or less a monolith with a RDBMS to encapsulate most of the business logic of my problem domain.

However, for various parts of my application that seem high-complexity, high-impact and non-competetive edge (such as authentication and credit card handling) I want to outsource to external services (Auth0 and Stripe). This brings with it the challenge of managing state, and consistency across various external services (on top of the state I manage internally).

The reason microservices is mentioned in the question, is because I believe these problems generalise from my specific case, to microservices.