I will recommend the use of a 2x8GB kit, two sticks run cooler than four it also puts less stress on the memory controller.
You do want dual channel function (the purchase of a 'kit' of ram will ensure compatibility between modules) as it offers a significant (not double though, maybe 20%) increase over single channel.
Note that Dual Channel and Double Data Rate (DDR) are not the same thing, any ram you purchase will be Double Data Rate (DDR3)