How to effective manage an actual department...(I will not promote)

My startup was in the right place at the right time, and we're seeing hockey stick growth. I was employee #2, the sole engineer who has been a freelancer pretty much my entire career. I currently manage a couple employees, and we have a Jira board, we do code reviews etc. But I'm about to be managing 10, 12, 20 employees. And I have no idea what I'm doing. I don't have corporate experience at the level a person in my position should have. VC's are starting to knock on our door, and I'm gonna have to act like I know what I'm doing or get shown that very same door. Does anyone have a course they'd recommend? This is really a managerial problem for me on how to manage an engineering team