doom-emacs-config VS ox-leanpub

Maybe take a look at my (messy) config, because I've got it set up exactly like how you describe https://github.com/ThomasFKJorna/doom-emacs-config (I'm using Doom though)

There's more customization for the indentation and getting rid of the stars etc, you can see that in my config: https://github.com/ThomasFKJorna/doom-emacs-config

I use Org mode to write books which I publish at Leanpub using my own ox-leanpub package. Leanpub produces nicely formatted books in different formats but it's a commercial service, so YMMV. In the past I have also used ox-rst to export reStructuredText, and then process it with Sphinx, which produces nicely formatted output.

I developed and maintain an Emacs package to export from Org into the markup and structure expected by Leanpub: https://github.com/zzamboni/ox-leanpub. This what I use to write an publish most of my books (https://leanpub.com/u/zzamboni). It works great, I can write everything in Org, and additionally Leanpub is a great service, run by very competent and friendly people.