i woudnt put
flax seed oil in a
postworkout shake. Fat slows the absorbtion of carbs and protein and you want them to be absorbed fairly quickly to replace glycogen stores and use the anabolic window of opportunity to its fullest.
As far as how much dextrose, its different for everyone as far as how many carbs are necessary to replace stores. Also the intensity and duration of your workout make a difference. A 30min workout is not going to need the same amount of food as an hour long workout for instance.