No, this doesn’t need a Fan Edit at all. Make an Extended Edition instead since the book is terrifying and intense.
The rock war and cleaning up the blood are in the book, but mildly different, which isn’t out of place at all. The most major suggestion is to read the book or listen to the audio version, unabridged. Yes, it’s supposed to be way too intense since the major characters are kids in this half of the adaptation.
The TV mini-series from 1990 omitted many things from the book since it was halved from the intended four episodes down to two. Yes, I would add more, as long as it isn’t redundant or conflict with the source material.
If anything, when both IT: Chapter One and IT: Chapter Two are released onto BD with a ton of deleted scenes and the longer cuts, make a version where it combines both movies to be more similar to the book in format. Of course on separate BD50s.
IT: Chapter One is one of the best Stephen King adaptations out there. This is literally a waste of time for a Fan Edit since it doesn’t need one and I’m certainly not interested.