the code is in the back of the manual of the game
Yes it is, but is better to buy the disc game from Amazon.com
At the moment Uncharted 3 is rated RP which you may see on adverts or posters,this does not give an age rating but what it means is Rating Pending. So it has not yet been rated but the other two games were Teen, 15 (And awesome) so I think it's going to be a 15 :)
Yes, she'll come up about halfway through. (I don't wanna spoil, but she'll come up in a foreign place)
If you are referring to the zombie-like creatures, they are explorers who were mutated by "the curse of el Dorado."