I havn't read thru everyone's posts, but I will like to add a couple of things.
Firstly, if you are trying to add muscle, do 3 sets of 8-12 reps. Anything more, you'd be building endurance, any less, you'd be building strength.
And yes it's good idea to do some legs and back workouts too.
And get some protein powder into you within 30mins of workout would be best!
And if you are just trying to build muscle, it'd not bad idea to stay away from cardio exercises when you do weights (before AND after).
And I do think, increasing a bit of weight and time working out helps.
Lastly, if you do have shoulder pains, or if you consider yourself not up for weights to give you a real good 'tear and repair' regime, I am not sure if building muscle is in your best interests.