I would add SpywareBlaster which is similar to real time protection in that it protects you while you surf.
Of course use the firewall. Be sure to see "allow an app or feature to pass through Win Firewall" + adjust as necessary.
If you have a router/gateway set it to WPA -2 with a strong internal password or key.
Also, I would use MBAM or MalwareBytesAntimalware which is a good malware scanner if kept up to date.
There are many combinations but this should keep you secure if you use the web safely.
I have been using win 8.1 pro since it was released to MSDN subscribers.
These are all I use.....
1. Windows defender, aka MSE, as realtime protection.
2 Malwarebytes free edition as on-demand protection, which I run it once a week to make sure.
I have not had any security issues.
If one observes the "safe internet surfing " guidelines, the above 2 will be enough.
If one is careless, no AV will or can provide protection.
If you want 3rd party AV for realtime protection, that is your choice.
Just one thing, Avast free edition v8 is NOT compatible with Win 8.1. It works on Windows 8 but NOT win 8.1. I said that with first hand experience.