Usually you should just wait until he's home at a certain time because he could be anywhere when he isn't home.
at fort mercer
Gaptooth ridge
you have to finish all of the undead unter missions before you can find him.
in gaptooth breatch and el materdora
It's in the same place as it is in the original Red Dead Redemption. In mexico
The retcher, Bruiser, and Bolter, along with regular type.
No you can't there is only one in the game.
You must finish all the Undead challenges in order to get the Chupacabra
Wild Feverlew: anywhere Prarie Poppy: Anywhere
No, you can only find it once I'm afraid
The four horseman are Death, War, Pestilance, and Famine.
A various amount: Snakes, Bears, Rabbits, Armadillos, Horses, etc. In the Red Dead Redemption: Undead Nightmare DLC, there are a few more species, and everything is "undead." Normal animals are not as evident, but their are: Undead Dogs, Undead Horses, Undead Wolves, Undead Bears, and a Sasquatch. Their might be some others, but these are the ones you are going to run into the most. Oh yea, and on Undead Nightmare, don't forget the zombies ;)