Yes,two AVs will conflict. Especially if one of them is Norton.

Number of malware in database usually cannot be counted that easily.
Some companies count every piece of malware even within same family, others count only entire family (Beagle A-Z for example), you also cant count generic and heuristic detection. So these numbers aren’t really important.

I think that number of Home Edition users is over 2 milions (or is this number for all avast! products? Alwil guys will confirm this hehe ;D )