A question about the literary relationship between Kafka and Goethe

Hello, I am someone who is interested in literature, of both Goethe and Kafka. I know that Kafka's attitude toward Goethe was great admiration, but I don't know precisely which works of Goethe that Kafka liked. I don't know any German, but from what I've read in Kafka's biographies and diaries, apparently Kafka greatly prefer Goethe's prose works to his poems, especially his non-fiction prose (Letters, Diaries, Travel Journals, Auto-Biography,....) Am I correct? I'm curious to know which of Goethe's prose was Kafka thinking about when he wrote in his Diaries that "Goethe probably set German literature back a few decades by the force of his style alone" (quoted from memory). And it looks like that Kafka found something common in both Flaubert (a writer whom Kafka also admired alot) and Goethe's art, too?

And if possible, you can recommend me some book in English that discuss (scholarly) Goethe's influence on the German language in both poetry and prose please.

Thank you very much.