Might as well put one fan in each place there is a holder for them, so 5. The case holds 80mmX25mm fans stock, but you may want to cut out the surrounding grills, enlarge the holes and then add 92x25mm fans. This would allow you to use quieter fans with more airflow.
I reccomend that you get a Rheobus and hook the fans to it. I would go with either 5 80mm Panaflo H1As or 5 Panaflo L1As. The H1As are louder, but on a Rheobus they will allow you to adjust between silent and a lot of airflow (39CFM Max). The Panaflos are only 24CFM max. As for a Rheobus, the Sunbeam at SVC is what I am buying here shortly and a lot of people like.
The Antec fans that come with the case can be used if you want to save money, but I would just go ahead and buy 5 matching fans.
Brian