Just to give an idea of how much filtration...
My 4000 gal rubber pond 40'x6'x3' -- http://www.planetcatfish.com/forum/viewtopic.php?f=25&t=29488&hilit=pet+catfish -- had small gravel substrate (1700 lbs; called river nuggets, various size, contained a bit of sand too) and 100 gallons of nylon mesh scrubbies for a filter media (~2000 scrubbies plus some filter pads). The pump was 2000 gph. I had ~300 lbs of fish in there at the max and had no problems with water. There were also a couple of 50 gal plastic tubs full of plastic plants that helped filtering too. Lots of air bubblers.
After extra-heavy feedings, I'd detect more than 0 ppm of ammonia next morning, so I just split them up in smaller but more frequent feedings.
Sounds reasonable.

