What is the proposed penalty for students that paid an essaywriting service to complete their papers for them?
The official punishment already has a fork, being the first time and honest can help them to get a suspension closer to 6 months than to a full year. Also, you can help them get a speedy process, so the penalty starts counting as soon as possible.

It is important that there is an official record of this event, so they can't pull the "it is the first time, I promise" again. They now have a record, and they know it.

This said, I can't believe they didn't know they were doing something wrong, so I don't think one should be very forgiving.