Hi, goranilic
I would use NOD32 Antivirus rather than Avast!. However, if you feel confident about your choice then it is OK. At least Avast is a better choice than AVG, because it has rootkit tool.
As for anti-malware software, I can say that you shouldn't rely only on Windows Defender. I'm not saying that it is unreliable tool, but is doesn't provide powerful protection against malware. Have a look at this comparison table:
http://www.2-spyware.com/compare.phpAs you can see, Spyware Doctor is the best choice at the moment. Windows Defender has lower ranking. Besides, you nay use Spyware Doctor and Windows Defender at the same time.
Windows firewall is fine, but not great. However, it should be enough to ensure sufficient protection against known threats. If you want more solid protection, then use PC Tools Firewall Plus (free) or Comodo Firewall.
Good luck!