Ask HN: Startup growing, best way to become company?

I am working on an app with some friends / family. We've all put in some money, split up what our ideal shares would be (i.e. 70/20/10), and after launching our app we're starting to gain some traction. We would like to become a legal corporation to protect us, and at the same time we need to do what is best for the startup. How the heck do I figure this out?