I would avoid combining with a 3rd party firewall as they often cause issues with file sharing, update process of some software including Windows Updates and, or are over-complicated (ie, HIPS alerts, Automatic sandboxing of trusted programs, blocking trusted websites). Also Windows Firewall on Windows 8 is a lot better than the days of the XP-era. A lot more free and paid AV vendors are switching over to the Windows Firewall for their security products, ie. Avira.
Before buying, I would recommended trial running at least ESET, Kaspersky or F-Secure, all offer 14/30-day trials. Alternatively you can use a Free Antivirus (but watch out for the catches), or stick with Windows Defender (built-in to Windows 8 and 8.1).
Windows 8 + (AV of choice) + Windows SmartScreen + UAC (default) + Windows Firewall.