2.I'd say that PJ didn't necessarily remove the 17 years gap, but rather that he didn't want the passage of time to show or to be important in his movie in order to give a feeling of urgency to the plot. We know Gandalf strides out of the shire after the party and travels as far as Minas Tirith and back again, we don't know how much time he's out by the time he returns to the Shire.
3.There were no Erebor dwarves, the dwarves who fled Erebor after the dragon's attack were scattered across the land or formed colonies in the Blue Mountains. I believe that recovered Erebor was taken largely by Iron Hills dwarves under Lord and now King Dáin. Of course old refugees from 60 years ago must have returned to the mountain from Ered Luin, Dunland and other places, but it is my belief that Erebor was colonized mainly by Iron Hills dwarves with Iron Hills customs under a king from the Iron Hills.