How do I stop feeling overwhelmed by a big project?

You can do the small moves already. What floods you is the whole thing at once, all the parts demanding attention before you have touched any of them. That overwhelm is not proof you are not ready. It is what a large task feels like before it has been broken down. A big project is never really one job. It is a stack of smaller jobs standing close together. Your mind sees the stack and panics. The way through is to stop looking at the stack and pick up the piece nearest your hand. You already know how to move that one piece; you said so yourself. So make the project smaller than your fear. Write down just the first step, the very first, small enough that you know exactly how to do it. Do that one thing. The size of the whole does not shrink, but your relationship to it does. You build the big thing the only way anyone ever has: one piece you already know how to handle.