If you're not interested in overclocking or achieving max performance, I'd skip custom water cooling. Getting max performance and the quietest PC are at odds, even with water cooling.
The closed-loop liquid cooler for the CPU is a good idea to eliminate noise. Though not necessary. A large air cooler will cool the CPU adequately and still be very quiet as long as you choose the right fan(s).
I would suggest, however that you skip the Accelero hybrid. This is a more or less half-baked liquid cooling solution as you still have a small (ie noisy) fan to cool memory/vrms. What cooler do you currently have on the XFX 7970? It it's the blower style, getting a new cooler such as the triple fan Accelero Extreme III
will get you just as good cooling, and shouldn't be any noisier, at half the price.
If you really want a quiet PC, I'd suggest looking into a case with good noise dampening. The Antec sonata isn't bad, but there are quieter cases now. For example, the Fractal define R4. I just did a basic build with one and the thing is barely audible.