For my future computer, I'm not sure whether or not I should get 8gb or 16gb of RAM. My friends all tell me that 8gb is already overkill but, I don't know, I want a few more opinions. Don't tell me to Google it either.
As for the OP, 8GB is plenty. 12 Is as high as I would ever care to go, and 16 is just a pure waste of money. Also, unless you plan on doing some pretty heavy over clocking, and have 4 or more HDD's and 2 or more GPU's, I would skip the water cooling and get a smaller PSU.