My tower unit media server has five fans and wasn't the quietest thing on the planet until I fitted air filters having become fed up with the speed at which dust collected inside.
A small number of big fans can be a lot quieter than a large number of small fans without any loss in cooling capacity.
My last server had seven 8-cm fans and was very noisy. The next one I built had only 12-cm fans and was much quieter. My current desktop is in one of those more recent PC cabinets that are equipped with a big 20-cm fan (or even a 30-cm fan), plus a few 12-cm fans. It hardly makes any noise at all, but the CPU and GPU and everything else stay very cool.
As for dust, stretching some women's nylons over the air intakes works really well. Bigger fans that move a large volume of air at lower speeds also seem to help reduce dust.