3 Make sure there are 4 identical flyers on 4 pages.
7 - "Nur die Papiergröße der Drucker-Einstellungen verwenden" (also see below)
12 > Check the option "Use only paper size from printer preferences" in the tab "Options" in the printing dialog.
14 See https://ask.libreoffice.org/en/question/34294/writer-42-how-to-print-two-a5-in-one-a4/