Are the InDesign files styled exactly the same throughout the 20 books (using the same classes consistently throughout the works)?
If so, you could come up with a set of Regex to help clean up a lot of the code. Then you can have a single consistent CSS file which can be used in all 20.
This is what I did at work for one of our quarterly journals, and now hours of editing has been wittled down to clicking a button to run a set of Regex in Sigil.
Most of the time is then spent:
- Coming up with the universal CSS file.
- Trying to emulate the look of the original document while sticking with maximum compatibility with most devices.
- Cleaning up code that the regex missed.
- Adjusting regex so conversion of future journals will be even faster. (This is VERY dependent on the original designer being consistent with their style usage).
- Fixing/regenerating images.
- Checking on an actual ereader.
If you want to send me a sample or two of an InDesign EPUB + original document (PDF?), I wouldn't mind taking a look.
My Background: I work for a non-profit economics site, most of my work is going from PDF scans -> EPUB, and I have completed 150+ books so far. I do not have any experience with Quark output (doesn't hurt messing with something new), and I have a tiny bit of experience with output directly from InDesign.