I would post this to a marine reef tank forum. Those guys are much more knowledgeable about complex sump systems. I do know that ball valves probably aren't going to cut it and that you might need to go with gate valves in order to have more precise flow control. And as far as loudness, you should look to something as simple as a durso setup or go to a bean animal setup which is more redundant. And you could look into ghost overflows along the back of the tanks to further reduce noise and cut down how many holes need to be drilled.