If u behind a router u don't need any firewalls, plus if an actual hacker would want to get into ur pc I don't think anything would help. Good Firewalls are hardware created and cost a lot! +1 for Spybot S&D. If u really want a good antivirus, and I'm sure u will get lots of different suggestions but "NOD32" is the best in my opinion, but its not free.
Cheers