Hello Saskia,
This is a great idea and will be a good initiative. But I would like to suggest to discuss this matter with Medium new CEO, Tony. He is a great and would surely guide us more into it.
If you have already discussed it with him and got the approval, i appreciate it highly.
I am saying this because medium is a bit strict regarding affiliate marketing and other promotions. People have lost their accounts in the past with little mistakes.
Hope you will clearify the point.
I am in.