I can't improve much on all this helpful advise (though I second Dan's reminder about manufacturer's specmanship), but if this will be a permanent fixture, you'll need to include filtering and maintenance in your plans. The annual Cleaning of the Pond at our house is always a fun-filled festival of fish capture, snail rescue and tadpole counting, accompanied by the pleasant aroma of algae and year-old bottom of the pond muck.
If you find your project to be too easy, you can always make the
water go uphill.