I’ve got, I think 6 if you don’t count the 2 on the CPU cooler or the PSU fan, which acts as an exhaust. (Or the gpu cooler for another 2).
That 1 noctua runs off the PSU direct, through the inline speed adaptor. Intakes run off the mobo fan control, exhausts run off the fan controller. Typically they all run at pretty low/quiet speeds. I’ve hit on a pretty good cooling throughout so the mobo run ones never seem to ramp up. Just the gpu and CPU fans. Occasionally PSU. If I want more air flowing through turn up the fan controller. My box is stuck in one of those under desk cubbies for the moment, so need a bunch of air moving through there to compensate. But since I hit on my current cooling plan all the case fans seem to just stay at the quiet base level, And my temps are fine.
Most of noctuas more recent (and more expensive) fans seem to be built for low speed. And all the schmancy new bearings help with that. (@anon89609066). In all but the cheapest fans the bearing doesn’t seem to be a major contributor to noise. Until they start to fail. All the frictionless fluid, magnetic, stainless this, magic shit bearings just keep the until at bay longer. A lot of the noise seems to come from turbulence coming off the blades and vibration, either against the case or disturbing the airflow. Rubber mounts minimize the vibration, And any stress on the bearing from the fan running unbalanced. Keeping dust out or cleaning it off preserves the bearings, And keeps airflow clean to minimize noise.
My oldest noctua is I think 4 years old. Still fine. Still silent. The newer ones have 2 years of regular use in them. Some of the fractals got loud after about 2 years, And were replaced with the new noctuas. The others have about 2 years on them now. Keeping them low speed and away from dust has kept them going just fine.
That heatsink is probably way, way over kill. Unless you overclock. I do fine with a hyper 212, with a couple of name brand fans attached.
Eta: Eh I crossed some stuff up. The PSU no longer acts as an exhaust. I’d always done it that way, but heard about concerns that drawing hot air from inside the case, through the power supply shortens it’s life span. So I figured I try flipping it over so it’s basically on its own loop. Cool air from outside the case directly out the back of the PSU. Things are much cooler and it’s fan rarely ramps up. Also I can’t recall where my 6th fan is living at, pretty sure it’s still in there. Plan was equal number of intakes and exhausts, use the fan controller to force the exhausts to run as slow as possible. Should maintain positive pressure for dust control. Then ramping up the controller as needed to equalize the pressure or make it negative for airflow.