QUESTION: How many books a year should I write?
It's become standard, particularly in paranormal romance and urban fantasy series novels, for the author to have the first three books printed in very short succession. I've seen several authors with three books out in three months.
The closely spaced books allow a synergy of promotion, word of mouth, the short attention spans of readers, and the addictive nature of readers to build phenomenal sales.
This method is so successful that sf and fantasy lines as well as thrillers now do the same thing.
The good news for authors, both traditionally published and self-published, is novels in short intervals are great for the career.
The bad news is the schedule is a physical, emotional, and creative monster some authors don't survive.
I know of several publishers who have told authors that if they can't produce on a fast schedule, the publisher isn't really interested.
You have to ask yourself how many books a year you can write and maintain your health, sanity, and your real life.
Editors and agents may insist that you follow such a brutal schedule of books, but they care primarily for their bottom line, not the price you will pay, so think carefully before you agree to such a schedule.
Also, remember that the quality and uniqueness of the books will probably suffer if you have no time for rewrites or creative time to think through your new book.
Even very successful name authors get caught in this trap so that their published books are in dire need of a serious rewrite and are so repetitive as to be boring.
NOTE: Some self-published authors who aren't required to produce particular lengths for their novels report the same success as multiple novels by producing a series of shorter, often novella length, works.