I am planning on starting a new character tomorrow who is a pickpocketing smooth-talker with a nasty habit of killing people . I will eventually join the dark brotherhood but I want to start with the thieves guild first to build up some skills.

Now my questions...
When you pickpocket someone do they ever get more items in their inventory ( like after a day or two ), because if they didn't then I might have to roam to other towns to make some money this way.
How many NPC's are there in the game who are un-killable ( i.e. quest related, and just plain made not able to die by Bethesda) because I know that in past games there were NPC's who no matter how hard you tried you could not kill them and I feel that it takes away from the game a little bit. And is there a mod out that removes this un-killable status yet? I know I can search the mods section but it is late and I don't have time at the moment to do this.

Any info on playing this sort of character is welcome as well, as I usually do not play the stealthy thief/assassin type.