There are ATMs in Dagestan, and there are not a few of them. You can pay with the card in supermarkets, hotels, shops and other places. But cash during the trip will also be required, you need to take a certain stock with you. Especially if you plan to stay not only in cities, but also in mountain villages or resort towns.
Charter flights are additional flights, unlike regular ones, they do not have a clear schedule. They are designed to transport a certain group of people. Most often, such flights are organized by tour operators to deliver groups of tourists who have bought a tour. The price of a charter ticket is less.