If you're going to surf the Internet, you should definitely have anti-virus. Windows 8 comes with free anti-virus software from Microsoft called Defender. It's not the best package available, but it's free and doesn't choke your system. Instructions here:
http://forums.anandtech.com/showthread.php?t=2325766
I'd also recommend installing Malwarebytes Pro ($25, but often goes on sale for $15). It has a realtime module for catching spyware. When used in conjunction with Windows Defender for anti-virus, you get a good pair that doesn't kill your system performance, but does a pretty good job of blocking spyware & viruses:
http://www.newegg.com/Product/Produc...82E16832562003
If you want to get serious about it from a browser perspective, switch to Google Chrome and create a shortcut on your desktop to Incognito Mode (this prevents cookies from being stored & prevents a lot of extensions from automatically loading, like toolbars) and then changed the Advanced settings to "Click-to-play" for plugins, so stuff like Flash, Acrobat, and Java don't run automatically.
That's my basic setup when I setup home computer systems. The antivirus is free; Malwarebytes is a one-time fee of $25. The browser's Incognito & Click-to-play Plugin settings help cut off other annoyances. So it's pretty basic & low-hassle in actual use.