@Mediacom87Thanks, I thought you had replied to my last question about the export. :-) That clears things up.
Yes, documentation requires a lot of time. Good luck with that! I hope your module can export according to multiple order statuses, too. I'd be very interested in that.
Thank you, @datakick. Unfortunately, it didn't work for me, even though I've tried altogether for about 2-3 hours, but it's OK. I'll find another solution. For others who want to try, some hints:
With these collections:
Ordered products
Orders
Addresses
I could get these columns:
Unit price
Unit price tax excl.
Country ID
Invoice number
Invoice date
Is validated
But that still means
you have to manually associate the country ID with the country (not sure how that works where invoice and shipping addresses are different)
the tax for the shipping costs is missing