So I'm building my first pc and I really like the NZXT case but it doesn't have a 5.25 inch optical drive in it, but i still need to get Windows 10. I've heard that you can by an external optical drive but that's more expensive. And then I heard you can use a usb to get windows but you need the product key also. So can you buy the product key by itself with spending $100? And when you use a computer to download windows off of for your usb. Does that erase everything from that computer? Sorry for the questions but I am very confused.