You might want to check memory online. It is quite cheap nowadays.
There are different reasons why you'd want multiple nics. Mainly, is for routing. You use one nic to connect to one network (often the iinternet) and the second one to connect to your local network. Or having multiple nics, to allow your computer to connect to the net through one, and other computers to connect to the net via your computer (thus, making your computer a router.)