For starters, I would never recommend actually buying an antivirus program. I personally use Microsoft Security Essentials (which is free) and does as good of a job as any paid program I've seen.
That looks like an awesome setup for you - just make sure the power supply is of a quality brand so that you don't end up with any fried components. E.g. Corsair (Not CX/CS), XFX, Seasonic.
Thanks, I've heard that some anti-virus software companies are responsible for releasing viruses. They also seem pushy with updates and upgrades. It feels like a scam. So I would rather use something from Microsoft.
I have a SeaSonic X-850? Is that ok? I don't mind switching if it means keeping the computer from frying.