Regarding the Enemy

New member, first post; a few basic questions primarily concerning the bad guys:

1) Gandalf and Sauron were both Maiar--angels for all intents and purposes. Now as I understand it, part of the Istari mandate was that the wizards could never use their vast array of powers to effect an outcome...theirs was to counsel/rally/etc.

That said, if Gandalf wasn't incumbered by the mandate and allowed to manifest as the Maia Olorin, would he have been as powerful as Sauron? Powerful enough to take him on one-on-one?

2) Did the majority of the inhabitants of Middle-Earth know what Sauron was (that is to say, a fallen Maia who had been corrupted by Morgoth)? If I had to venture a guess, I'd assume that it was pretty well known by the Elves, who'd had real-time interactions with the Valar/Maiar, but what about the other inhabitants?

For that matter, was anyone fully aware that the wizards were also Maiar? I would think that some of the more important Elves (Celebron, Galadriel, Elrond, Cirdan) knew, but I can't see too many others knowing, because it's not like the wizards ran around announcing their true identities to everyone they met.

3) By the time of LOTR, the Valar had long stopped directly intervening in Middle-Earth affairs. That said, if Sauron had reclaimed the ring/regained all of his power, could the Valar have still personally unseated him if they'd gotten super-****ed (as they did with Morgoth).

4) Regarding Morgoth: as Melkor, he was little short of a fallen god and was unmatched by any being in Arda (save Manwe, possibly?). Over time he bled a lot of his native power into the world, weakening himself to the point where--though still immensely powerful--he was confined to a terrible form and apparently unable to repair injuries (Silms burned his hands, Fingolfin left him limping, an eagle tore some chunks from his face). Is it feasible to suggest that perhaps one of his lieutenants--Sauron in all likelihood--might have tried to overthrow him; or was he still too powerful for something like that to happen?

5) Last question: was Ungoliant more powerful than Morgoth? It seemed to me like she could have done him in when he refused to cough up the Silmarils, were it not for the timely arrival of the Balrogs.