This is a complex question.

Consider a 200 page book sold 2x ways...

1) Amazon: One time sale price of $20 - 30%.

2) Split 200 pages (at an average 200 words/page) split into 200 blog posts which generate profit/hour using either digital marketing + email marketing + direct mail marketing.

Let's say each page generates $1000/month income... so...

200 * $1000 == $200K/month income.

So $20/once verses $200K/month...

First question about book publishing is purpose of the book.

Tip: Smart Marketers never, ever, ever consider publishing a book for income.

There are many other reasons to publish.

Income is never a good reason for publishing.

Start with your profit/month, then number hours/week you'd like to work, then you'll generate a clear publishing path, along with your publishing calendar.