How do I oversee the whole financial function without overwhelm?

You can close the books, and overseeing the entire financial function feels like a different and overwhelming thing, going from doing the work to being responsible for all of it. That leap is real. Executing a task and owning a whole function are different jobs, and the weight of the second one is what you're feeling. Overseeing isn't doing everything yourself, and that's the shift that unlocks it. It's making sure everything gets done well, through systems, through people, and through knowing which few things you must watch closely and which you can trust others to carry. The overwhelm comes from trying to hold it all with your own two hands instead of building the structure that holds it. List the main pieces of the function, then mark which are truly yours to own and which belong to someone you can rely on. Start handing off, one at a time. You don't have to do the whole function. You have to see that it works, and that's a skill you can build.