How many students are too many for a first-year teacher?

Teachers are heavily underpaid and underappreciated. We send all of our children to be with them for most of the day; they are responsible for keeping them alive and untraumatized, educating them, and keeping them healthy and happy. They have to plan how to teach each individual class and student, because everyone is different. They even sometimes have to get their own school supplies for the class with their own paycheck. When are they expected to have time for their own life, mental health, or happiness? 

A first-year teacher is struggling with this exact dilemma, and the school year has only just begun!