Where do I start with the FDA and medical regulations?

When something looks like a maze, the fear is not really the walls, it is not knowing which turn is first. You do not have to understand the whole system to take the first step. No one who navigates it well started by seeing all of it at once. Start with your own product and your own question: what are you trying to get approved, and what path does it fall under. That single anchor shrinks the maze from everything to the one route you actually need. Most of the map is other people's problem, not yours. Find one guidance document that matches your case and read just that, slowly. Then find the one person, inside your company or out, who has walked this path before and ask them what they wish they had known. A maze walked with a guide stops being a maze.