I can't comment as to most of this, i'm sure others will.
BUT if you have rounded-forward shoulders, while addressing rear delt and overall back muscle relative weakness is a great idea, you also should:
1) Practice perfect posture (like in the military, chest out, shoulders down and back, tense your gut) at all times
2) Work on foam-rolling and stretching your body. Problems areas for me in upper body were pec minor, lats, supraspinatus (dig inside your armpit to get this) upper trapezius. Also do thoracic extensions. Reducing the 'tension' (tightness) in these areas led to less forward pull, allowing my back muscles to pull my upper body into a natural alignment.
In fact, foan rolling and stretching the whole body, from feet, calves etc on up would be a great idea. It really does work.