On my case, I have 2 120mm fan slots in the front of the case, 2 120mm fan slots ontop of the case, and 1 120mm fan slot at the back of the case. Should I fill in all of the slots? Or should I buy 2 or 3 fans. If so where do you recommend positioning them? Also which orientation do the fans need to be in? Which fans need to suck air in or blow air out?