I wrote a big thing for this yesterday but lost connection. I think they were updating the site. Anyways, spawn locations.
Predators and prey I believe will be biome specific, with some overlap.
No zombies other than zombie dog (even that I don't want lol).
Animals dens. Well, only for animals which would normally use a den. Like wolves. Not all use dens. They should sense the players presence and not come out of the den if the player is close, they should wait until the player is long gone. This way players can't camp the den and kill them easily as they come out. Dens should be protected so they can't be destroyed or accessed from below via mining etc.. But then, as you can see.. there are issues with having dens. So maybe just having them spawn in the world is best.
@red51 One thing is for sure. Devs, make sure animals don't clump together in one spot. They should be dispersed throughout the biome(s) they spawn in.
I hope predators will be drawn to kills you make, and also to your livestock in your farm. But, I want so badly that predators also make their own kills on prey. And eat them, meaning if you come across a kill, the meat is gone.. maybe you just get some leather from the body.
Birds/bats - I hope they do not despawn. I hope no animals despawn. It would be better if they go to their nest during the night. Owls would do the opposite. And bats would come from caves during the night.
Where monsters spawn. This has been talked about a lot. I would like to see them in dungeons and on the surface in temples and ruins etc.. not roaming around on the surface though.