Wadi Musa and Petra go hand in hand
You can't visit Petra without being in Wadi Musa too. Petra is only the old city and there is nothing to it beyond that. Wadi Musa is the city directly attached to it where you will find all the hotels, restaurants, etc. It's also where you will find all the people who live in the area. No one is allowed to live in Petra except the bdool.