Non-sense - if a historian were treating the gospels as they would any other piece of ancient history they would conclude that there is insufficient evidence to make any historical judgement on any miraculous claim, as Ehrman explains.
Not true. They would conclude that the miracle didn't happen. Did Jesus turn water into wine? Of course not. That would have been well beyond the technological capabilities of the first century (or the 21st century).
Did something happen that led people to believe that Jesus turned water into wine? An elaborate conjuring trick, perhaps? Sending out to his mate, the wine merchant, for more wine, perhaps? Maybe. These are questions that are up for debate and may not be answerable with the evidence we have, but the historian
can should discard the possibility of an actual miracle because the historian is as bound by methodological naturalism as any scientist.
Whether they believe, as a believer, is a completely different matter to whether they accept something as a historian on the basis of historical evidence.
Yes and, in fact, even Christian historians are perfectly capable of compartmentalising their faith when they are doing history. Almost all of the work done on discrediting the gospels as reliable historical sources was done by Christians. It was a Christian who came up with the idea that Matthew and Luke copied Mark. It was Christians who dated the gospels to after around 70CE. It was Christians who analysed Matthew and found he cribbed loads of stuff from the Old Testament (probably deliberately).
The dating of the gospels is interesting in this regard. They are generally dated to around 70CE or later partly because they prophesied a real event, namely the destruction of the Temple. The Christian scholars could have said "that means Jesus was good at prophecy" but they discarded that belief when writing their scholarly papers on the dating of the gospels and went for the obvious to non Christian people explanation of the gospels post dating the Temple's destruction.