[Karellen]

I set an Artist Information folder, and created subfolders for each artist using the Export function.

Perfect.

Is it requiered to have a .nfo file for each artist too?

No, not necessary. You can have artwork without nfo files.

Must the artwork files have a specific name?

Yes. I guess you have not read the guide. See here... https://kodi.wiki/view/Music_artwork You need the code as shown in section 2 and naming as shown in section 3