Cheers, that fixed most part of it! 
Good to know a thing like that exists also for Shopware
Page now loads fine, and in the back-end the categories load properly. In the back-end I can also see the product attached to the category. Only on the front-end there aren’t products visible. I’ve tried adding the store in ‚visibility‘ because it was blank, but to no avail so far…
Another idea perhaps ?