@clarkej Thanks for your pointers.
When I now read @umair talk about “good demo data” on demo.erpnext.com here I wonder if this has been lost since April 2017? The list of customers, items, quotes, reports and all of the things that make an ERP system stand out seem to be missing on demo.erpnext.com today. Am I missing a download link for “Wind Power LLC” for demo data? Where is it? How to import it?
I have also read this post:
It is largely technical and does not give an answer to my question, how to optain good test data. However the screenshots in this post of @clarkej seem to indicate that there is test data with enough samples available somewhere. 
#iamstuck