As an environmental science student, I should probably go back and read this thread when I have time. But I gave it a quick skim. Anyway, just want to say a few things real quick:
Things you can (most likely) do today to help:
-Eat poultry instead of other meats. Healthier, and more feed-efficient to raise. Plus, it often costs less at the store. Just pay attention to where it comes from, though.
-If you have to run your tap for a while before the water gets warm, put a bucket under it in the meantime so you can save all that cold water for other uses (watering plants, cleaning, or drinking if you put it in a kettle/filtered pitcher. Whatever you use water for.)
-If you have one, check the power requirements on your dish washer. Chances are you probably actually use less resources washing your dishes mechanically than by hand.
-Remember that humanity's impact on the planet is, for the most part, the sum of all our individual impacts, so making small changes to your life, and encouraging others around you to do so (don't be insufferable about it though!) can go a long way.
Things to keep in mind:
-Positive/Negative feedback cycles, look them up! They're key to understanding the mechanics of the environment, and its immense complexity.
-The big picture is never simple, but there is hope.
-Seafood will never be sustainable without either a reduction in demand, or switching our methods from hunting (that's what fishing is, even though its large scale) to farming (which, of course, has problems to solve before it could be sustainable).