With 120mm fans on the heatsink and the PSU I wouldn't think noise is going to be much of an issue. I wouldn't get more than 2, and probably only 1 fan that I would set up as an exhaust fan at the back of the case. That's what the PS3 uses. My WD Live Hub uses an even smaller fan than that and it's virtually silent. You'll probably be ok without any other fans, but you could always unplug 'em if they end up too loud.