1: Correct
2: For now just uninstall AVG using the removal tool from here, Windows 8 and 8.1 both have an updated version of Windows Defender.which offers the same real time protection as Microsoft Security Essentials so you do not actually need a third party AV, just make sure that it has been automatically reenabled in the Security Centre.
3; AVG is a strong contender but it could also be a Codec, it is a process of elimination I'm afraid and that is why I have gone for one of the usual suspects in AVG.
You are welcome