You are making the shakes correctly... I have Isopure vanilla which calls for 2 scoops and 10 oz of Water... so when i use 8 oz of milk they taste thicker. I will say that if you are using milk you can get simply smart milk 1% or Fat Free which tastes like whole and 2% respectfully. These milks really do work and were recommended to me by the Dr. Office.
As for more food, I dont know your pre-op diet, my Dr. does not mandate one but says that I can't gain and should try to lose.
But most importantly try not to THINK of food, because i suspect that is in fact what is making you hungry. This stuff is like drugs, you have to just quit it and avoid situations in which you previously OD'ed (to run with the metaphor).
I am getting cut monday so I can report back post op and I am in the same boat as you, just trying to get healthy.
Let me know, i'd be more than happy to share my Dr. handouts with you.