So, the reason I asked if you bought the fans yet was that if you have, you could simply read the current draw on the fans and size your power supply accordingly.
You will want to buy fans that all have the same voltage rating and wire them in parallel. When figuring out how big of a power supply you need, you simply add up the current rating of each fan.
guy has a lot of cheap fans.
power supply would power 2-3 of those same fans nicely.