protein supplements can be usefull. It all depends on your diet though. I rely heavily on protein supplements because I need alot of protein and it is not easy for me to eat all my protein. The supplements are very convienent, no cooking, no cleaning.
It is best to take your protein supplement post training as you want quick absorbtion and food doesn't cut it there.
I think you are better off with a powder rather than the RTD, from what I understand the protein does degrade when it is in liquid over time.
I would suggest Optimum 100% whey (very economical), if you can afford it VP2 by AST is one of the best.
As far as separate amino acids, you don't need them if you are taking in enough protein. Your whey protein powder will cover your amino needs. Amino acids are broken down protein.