'Veggie' Filter

I need some information on what a 'veggie filter' should be. Some say that
the surface area should be 10 - 20% of your pond. Others say that it should
be 10 - 20% of the pond volume. Which is correct.
Also some say not to use lava rocks, others say it's okay.
What about water flow? How many gph should it have?
Should the pond water enter from the top or the bottom?

Here is what I think I am going to do:
Pond size = 1600 gallons
'Veggie Filter' = 225 gallons (2x10x1.5)
GPH Flow = 400
Pond water will enter from the bottom and cascade out the top like a
waterfall.

Will this work?