Yeah it would have been counter productive if your shoulders and chest were making your back look even worse, which they arent cause they themselves lack serious size.
Its good to hear you are going to do the routines i told you about, but as for your back rounding on squats and DLS. It happened to each and everyone of us. You just dont use any weight until you practice the form.
I started off very very skinny, even worse then you are and it was harder for me to add weight cause besides having the thinnest limbs and being a hardgainer i was also 6'5. But as soon as i incorporated a good diet and compound lifts that work the back(from traps all the way down to hams) muscles i noticed great even gains.
I also advice you read up this article it is perfect for your posture worries and to implement this plan it wont cost you any more then 10 bucks :
Keep lifting and eating. And get back to us with good results.
PS: If you need bulking tips read up Barrs article: http://www.T-Nation.com/findArticle.do?article=05-163-diet