How many letters does the top answer for “composer of sister act” have?

The most common answer is goldberg (8 letters).

Crossword clue: composer of sister act

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

goldberg 8 letters wd-fact-v3

United States cartoonist who drew intricate diagrams of very complicated and impractical contraptions that accomplished

composer of sister act 2: back in the habit 60% similar → goldberg

author of sister act 50% similar → goldberg

wrote sister act 50% similar → goldberg