You can never have too many.
If a nation has firearms running around on the streets unwanted and unloved, that nation has too many firearms. Unless and until we reach that point we don’t have too many as a society. (and I don’t think we ever will, there are too many people like me who are always willing to give a good home to an orphan gun)
An individual can have too many guns. Houses do have limited volume and structural capacity. (If you cannot fit another gun in your house or your floor joist have passed the breaking point, you have too many guns.)