Great story, I like it. I disagree in one of your comment: modeling the microservices [...] are the tasks of the senior developer or team lead.

I think defining the contract, in a contract first design model, is defining the microservice. In this way, the task is an architect role. In my experience very few developers are concerned by loads, call numbers and so on. I do not think they have the big picture to slice.

By the way, those are my two cents.