perfect @nathschlaeger sounds good. I agree with you.
in your case @Dor 's approach for using embeding notes to later export to pdf is a genius approach that you might benefit from.
If not the online converters / apps might be what you need.
I agree with you though, plaintext is a great idea for writing a book, I wish it was a more popular approach, just in case you are interested org-mode is also plain text and 100x more powerful than markdown with some great features for book writers
Perhaps you might find this awesome lecture useful
I recommend org-mode for long format content writing to keep things really organized and easy to navigate.
Eventhough markdown allows for this type of writing (specially when used with a powerful tool like obsidian) org-mode will no doubt save you a lot of formatting and structruing time (but it does have a learning curve)
Just a suggestion, but yeah If you’ve used .md before for writting a novel then obsidian would be a great choice!