Ask HN: Bringing in a finance guy CFO

My cofounder is the business end of our startup. I'm the tech. He's been talking to his professors in college and one suggested we get bring in a finance guy. My question is, at what company size is a CFO justified? And what benefits, what can such a person do, that we can't do for ourselves?

I think it's way too early for us to be worrying about this.