The P160 is more than adequate. You could put a black ice or thermochill radiator on the rear 120mm fan spot easily. I know because I've done it before.
The only things that get turned on are the pump and fans and their configurations can vary. Normally the fans are connected to the computer's PSU. The pump, depending on its design, can be plugged to the computer's PSU or to a 120V source or to a completely different source. I have a Swiftec...
I have some pretty high temperatures with my Maze 4 kit on an Athlon XP 2500+. It's running at 42°C idle (my SLK-900A keeps it down at 34°C) and I think it's because of my pump (a Hydor L30).
I had a PowerPlant but the second time I turned it on, it pretty much exploded (blew a fuse, too!)...