Matt just to let you know, I decided against my original design. There was too much concern about flow rate, and the pump running dry. I did however come up with a design that would work. It's pretty similar to what you suggested.
My pond will be 2600 gallons. As you suggested my 3" bottom drain will gravity feed a settling chamber that will be no smaller than 55 gallons. I will have an external pump hooked up to the out flow of settling tank that will push water into a 100 gallon skippy bio-filter. The filter will also act as the water fall.
Here is a link for building skippy filters.
http://www.skippysstuff.com/biofiltr.htm
I have other links for bottom drain and settling chambers if anyone wants them. Man I can't wait to start digging.