JLPT is a test for the reading and listening ability, not writing. N1 might not be enogh, or N2 might be enough. It totally depends on the writer or the works.Do you have to be at around N1 level to write a Japanese novel or a story?
The total amount of used kanji has nothing to do with the works. There are novels or poems for adults written only in hiragana, or ones for children with many kanji (there is no problem for that since writers can put okurigana for difficult kanji).There are so many Kanji to be used if a writer writes a novel in Japanese, correct?