Joe,
Don't despair about the size of your pond. You can grow some really exceptional fish in a pond that size. You may not have as much quantity, but you can do a LOT with the quality.
The best way to incease your O2 levels from a waterfall like you're describing, would be to find a way to take the anoxic water off the bottom of your main pond, then make your 10 X 10 pond full of cattails or some such other macrophyte. This will give you both increased oxygen and trap some of the nutrients. This will also improve your carrying capacity of the .25 acre pond.
What kinds of fish are you hoping to grow. I love it when other pondmeisters have smaller ponds like this, because I can really relate.
If I'm not mistaken, the water that is pumped from the bottom of a pond isn't any more energy expended or net cost to taking it off of the top. The "head" remains the same. (Am I using that term correctly?)
