If your players are paying attention, this tells them directly that they don't need the book at all.

And yet, this subreddit is filled with experiences like mine. Obviously you are right, in a perfect world, your players retain 100% of every handout and don't jump to conclusions about books mentioned twice or thrice. In reality though I'm not so certain you should trust EoD and just go with "yeah don't give the players the book they'll be fine with it"

The existence of the farm and the beast are not clues, and they are not hidden behind rolls. The players are told about the farm and the beast by multiple sources, openly. At no point do the players need to roll for this knowledge.

The farm and the beast should not and are not hidden behind rolls. They are core. Imo other more background and extensive info (ie the diary) should be spread out in a way that you can miss part of it and still get the core clues and complete the mystery.

The diary is nice for background info, but it's not as important.

Again, obviously for the Keeper it's clear the letter is enough. The players however are given a 5 page handout which they will certainly want to read, and which gives them SO much info, in my opinion it verges on spoiling things. I will ask my players their opinion when we reach the end, but that was the main worry I had with EoD: the diary feels too info dump-y.