tl;dr - I don't think Writer can do what I need. I'm afraid I've come to the decision it's not really suitable for writing books, at least not if you want to produce multiple formats or layouts.
I've just spent a week learning about Master Documents.
Unfortunately, because the natural (most efficient) way to use Writer is to use direct formatting, I found from my experiment that the body of my document is rife with apparently random stretches of text that's been directly formatted:
I wrote all this, yet I can't imagine why *any* of the text that appears as 10.5pt inside the 9pt text was directly formatted.
Sadly, the amount of work needed to correct that would be absurd. Far higher than I'm ever likely to save from having a single file in which to make corrections, rather than making the same corrections to four separate copies.
I can't even see a semi-automatic way to remove the direct formatting. Just finding it is difficult - though I could now use a master document to see the DF text by manual inspection.
Now, given that I use only three character styles, Writer's design decision to create a new unnamed character style whenever DF is used, is exactly the reverse of what I want.
I can't see a way to remove all direct formatting, since I need a function which would remove it all without changing the visual appearance: in other words, a way to map the DF text to an existing 'base style' (regular or emphasis). Without that, I'd be looking at I think hundreds of hours of mind numbing, error prone manual work.
I think the design of the direct formatting feature of Writer ("assume the most complex interpretation is what the user desired, rather than the simplest"), is going to be the issue which finally pushes me to find some other word processor, after using Writer for approximately 15,000 hours. I find that sad.
