If you are hard-wiring your PC into your modem/router you probably wont need a wireless card right away.

As for your sound card, most motherboards have them built-in. Before you buy a sound card see how the motherboard's sounds and if it isn't up to your liking you could later either buy an internal one that will slide right into a PCI or PCIex1 slot OR and external card that plugs right into a USB.