Hello Norbert. Thank you for your answer it helped drive my thinking in a good direction.
On KVK website they mention the following 3 criteria with my understating of them.
1) You deliver goods and / or services. For example, you sell bicycles or you are a photographer.
On medium.com a writer is not commissioned to write specific topics. One gets paid if and by the reader, depending on values of the articles provided. Technically this criteria applies but not as for a ghostwriter.
2) You ask a more than symbolic fee for this. For example, you invoice the costs and the hourly rate.
What is the symbolic fee? I couldn't find any threshold or maximum. Is your example of 250 euros per month based on some official rule?
3) You participate in (normal) economic traffic. For example, you photograph on behalf of a client and not for family and friends.
This one is clear that as a writer or with a podcast one dose participate in an economic exchange.
I am still confused by these criteria. Your remark about the expected time and amount helped clear some fog but not all.
For now this will be a hobby that might get a max few hundred euros per month. Which will be anyway declared at the end of the year in the annual tax declaration.
I think I will not register for now.
Thank you again for your help.
Kind regards,
Bogdan