How do I set sales territories and quotas when I have no idea where to start?

The task landed on you and it feels like there is a right answer you are supposed to already know. There is not. Territory and quota design is a set of judgment calls, not a formula hidden from you. Once you stop looking for the perfect answer, the work gets a lot less frightening. Start with what you can actually see. Where are your customers, how much work does each area really take, and what did each person sell last year. Real numbers, even rough ones, beat guesswork every time. Build from what is true, not from what you imagine fairness should look like. Draw a first version, then test it out loud with someone you trust before it goes live. A plan you can explain in plain words is usually a fair one. You are not expected to get it perfect. You are expected to start with reason and adjust. That is enough.