Here in North FLorida, we are a multi line GM store. My previous warranty administrator averaged 3500 / month with the job assignments you mentioned. Did not have to cashier unless the office was very short handed. We had to let him go because of an attitude problem with the techs and management. Currently have not replaced him.
Trying to process thru my Service Manager & myself. Looks like we will have to hire before long.
Good administrators are worth more than dealers want to admit. They help collet a lot of $$$'s.