My thoughts are 15 gph, down 4 1.5 meter long gullys. I have no specific preference on type but thought submerged would stay cooler. Wattage is as low as possible, the first build will probably be grid powered but ideally a 12 volt dc pump is the goal, lowest consumption possible. For now a stable pump to experiment with is fine. Have given no thought to inlet size etc, would appreciate some input if it makes a big difference.