How many letters does the top answer for “author of northanger abbey” have?

The most common answer is austen (6 letters).

Crossword clue: author of northanger abbey

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

austen 6 letters wd-fact-v3

English novelist noted for her insightful portrayals of middle-class families (1775-1817)

wrote northanger abbey 50% similar → austen