Thanks for the questions on Stone!
To your questions,
1) Worldly Desires' ability is not considered to be a draw hand bonus.
The key thing with respect to the next two questions is the Location of the Shootout, not the location of the dudes in the shootout. So since,
2) The location of the shootout is not at home, only the shooter contributes to draw hand bonuses
3) The location of the shootout is at home, so you get the full contributions towards draw hand bonuses. So the dude with the buffalo rifle, who's at an adjacent location, would also contribute too.