It's (quite conveniently) directly under the "EC" in Beecher's Hope.
Being undead is not alive
a zombie
whatever you want.
It is not known but i assume around 20-ish.
No because Undead Nightmare is essentially a whole different game. You can only play as his son Jack at the end of the regular Red Dead Redemption.
its on Undead Nightmare
Then you become a zombie and that's it you probably didn't do the side missions
It's seperate to the original Red Dead Redemption. You can tell straight away as John Marston is still alive.
You cannot get Red Dead Redemption - Undead Nightmare on the PlayStation Portable.
No you can only use them in the undead nightmare.
Because people prefer him to Jack Marston so Rockstar games decided to use him.
No you cannot join with the zombies in undead nightmare