What a pain. I believe I’m finally getting this nonsense sorted out. Here’s what I had to do:
After the intro text, add a manual page break which also resets the page number to 1 and switches to a ‘first page of chapter style’ which has the page number as a footer but no header.
Add a ‘successive pages of chapter’ style which is the same as the first page but with the header. Make that the follow-on style for the first page.
Of course Libre Office lets you use a hierarchy of styles for paragraph styles but not for page styles… because… no, makes no sense to me either. So if you change any of these styles you then have to manually change the others to match. Stupid.
And, of course, that doesn’t work when exported to Createspace. It seems to use the first style exclusively for the whole of a chapter and ignore the style change. Now I’m trying to export as PDF and see if that works any better.