React is desirable because: it's a skill in demand, and can help make things easier.
However, it also requires some basic JS knowledge first so it can take a while to get started on that.
Also, React can be used to make a SPA. But the calendar library is already doing some stuff that's like a SPA. And Node/Express can also help you make a SPA and we know that we're going to use Node/Express.
Problem / context: