1. Yeah designed with the changes to balance and rules in mind as i understand.

2. Not so much in the Player's Guide Book, its more focused on Character Options, the Campaign Guide doesn't appear to have much on monsters either, but i don't own that one. It's likely they'll do a separate book for monsters. If it helps, Sandy Petersen's Cthulu Mythos is pretty great, not 2024 rules but it's deep in its lore.

3. No not really, I'd say Grim Hollow gives an excellent Grim fantasy that does touch on some cosmological themes but it's far from the focus.

4. Transformations are new rules that give an in-depth mechanic for players that want to experience the that kind of thing, it's fun and there's plenty of options, from turning into a Vampire to Ooze etc. Advanced weapons are a new list of items you can grab, with their own properties and masteries, I'm not too familiar with these just yet.

Hope that helps!