Most fans use anywhere from 100mA up to 1000mA (1 amp). Take a look at the fans you want to hook up and find out what the current rating is. Then add up the current and make sure that it does not exceed the current rating of the motherboard connectors (usually between 500mA to 1000mA, should be listed in your motherboard manual). As long as the total current drawn by the fans is within the spec for your motherboard you can use fan power splitters to connect multiple fans to one connector.