1) No, do not worry about defensive stance. A pitcher has far too much to worry about than fielding come-backers. For one, the odds are very low during the course of the game that a combacker will occur. Second, to get in the "proper fielding position" requires a weight shift from a) over balance position to slightly left (falling off the mound slightly.. this is actually okay), to b) stepping to right of mound (to get ready for fielding position). Advocating "b" seems a scenario for short-arm action.
2) Elbow slightly low at foot plant.
3) I don't like the stepping back behind the mound during the windup, a common approach of youth pitchers. It screws up the balance and timing. Rather, I'd say stepping to the side is better, allowing the pitcher to stay more balanced and rythmatic.
4) Release out in front more.