Couldn’t give an answer to your first question, but can provide a "nope.’ to this one. Even with established, conventionally-published writers I prefer a whole novel all at once rather than serials. “Fan fiction” I don’t touch at all.
I touch a lot of Fan fiction. Wait, that came out wrong…
Anyway, I’m reading a bunch of novel-length fics that are currently Works in Progress. One started with a relatively short PWP (smutfic), then the author went in and developed it more, and she just finished the third novel of four in the series. Total words so far - over 1,000,000,000. She starts the fourth novel this Sunday, and I can’t wait to read it!
(Message me if you want a link, it’s really good Drarry)