the radiator is on the end, the cpu gets the fresh water from the pump first, anything else in is in the middle.
I'd say that prio 1 is to have the reservoir just before the pump. Prio 2 is to have the water rotate in order radiator -> CPU ->
GPU -> radiator, but it doesn't really matter where in this loop the reservoir/pump combo is placed.
This advice is key to making a system more silent and cheaper. ..., just get a larger radiator, biggest possible that holds the most water.
Bigger radiator won't make it cheaper, but it definitely will help in reducing the required fan noise.
edit: I just looked at the radiator. It is not designed to quietly cool 2 major components.
Asetek rated their single radiator as capable of handling up to 400W, which is probably true as long as one doesn't expect more than "won't overheat when a noisy fan is used".
Unless the room temperature is very low I don't expect a 900rpm fan to suffice for cooling your components. It should rather be a 2,900rpm fan, at which point we're well away from "quiet".
There are really two ways to reduce the need for noisy fans:
1) Larger radiator. Possibly placed outside the case, if you want the case itself to stay neat.
2) Larger reservoir (and thus more water in the system). One key advantage of water cooling is that it carries a large thermal inertia that makes temperature changes in the system much slower than with regular heatpipe cooling. With heatpipe cooling you need to cool off the near instant thermal power, whereas with water cooling you just need to cool off the average power taken over some time, and the more water the longer this averaging time "window".
In normal operating conditions you rarely have the CPU and GPU operating both simultaneously at 100% for more than a few seconds at a time, so averaging the work load over several minutes will result in a considerable lower value. With a water volume like 10 litres or more, starting at a 20C temp, you can leave the computer running at 100% load for an hour or more without cooling the water at all
and it won't overheat...