Its not so much the silver itself that kills the bacteria, but the ionization of it. So it doesn't overly matter how much you have. That being said have a decent amount, coil it around your finger a few times, that much-ish.
Best place would be around the downstream radiator port, as chances are thats furthest away from any the pump and PSU, some tests around here have shown that the closer the silver is to those, the faster your tubing will cloud.
Though really, any place where its in contact with the water and wont get into any blocks or the pump is fine. I just have mine sitting in my reservoir.