Gandalf

[Nunc]

I have been reflecting...

What happened to Gandalf when he fell in Moria? He tells Legolas, Aragorn and Gimli: "Long time I fell, and my foe fell with me." The balrog turns into slime, Gandalf holds onto his heel and so manages to find the lost stair, and then ensues the fight on the top of ZirakZigil (whatever it's called). Gandalf then passes out of thought and knowledge.

He talks about wandering... He obviously comes back with a modified (?resurrected?) body which is slightly translucent. He also says something about "forgetting much which I knew, and remembering much which I had forgotten".

What does he mean by this? Where did he go? Did he return to Aman, to Manwe (Olorin being one of the Maiar of Manwe... Manwe as lord of the air maintained contact with Middle Earth even though the rest of the Valar had forsaken it after Morgoth ruined it, through the services of the great eagles and other birds of the air. This is why Gandalf has such influence with the Eagles...)? Did Manwe send him back? Or did Eru Illuvatar?

What was the nature of the choice of those Maiar who elected to go to Middle Earth to aid the free peoples against Sauron? Did they assume mortality/immortality of the kind of the elves? Or were they completely different?

Why is it that Gandalf before Moria seems less powerful than the White Rider (Gandalf post Moria)? Where does his power come from? Why the injection power at this point?

He says to I forget whom, "Even though the [wars with Sauron/quest of the ring/defence of MIddle Earth by Gondor and its allies etc] should fail, my quest shall not have fully failed."

What does he mean by this?

On the other hand...

Gandalf is of the Maiar, as are all the Istari. Sauron is also of the Maiar of old - originally of the folk of Aule, but then aligning himself with Morgoth.

If this is so, why has Gandalf himself not the power to confront Sauron? Is it that evil somehow makes a spirit more evil and more powerful than it was otherwise?

Moreover, are not the balrogs also Maiar? When the Trees were murdered, and in their place Varda created the sun and the moon (single fruits of each tree), the sun was given to a "female" Maiar who was a spirit of fire... A good version of the balrogs, a Maiar not tainted or twisted by Morgoth.

Why then is the balrog of Moria too much for Gandalf?