[Raynor]

Hmm, wonder if this is why he too made himself a 'ring of power'? To help re-house himself?

I don't think that his power, and therefore the power he could have poured into the ring, was anywhere close to Sauron's, so as to allow him to rehouse himself; and it is mentioned in the LotR preface that he still had missing links in his ring-lore. I believe that he, like Sauron, never contemplated his death, and therefore had no planned backups.

I doubt he could have been 'destroyed' by the Valar

Perhaps you skipped my post #23

Originally Posted by Letter #211

The indestructibility of spirits with free wills, even by the Creator of them, is also an inevitable feature, if one either believes in their existence, or feigns it in a story.

I was under the impression from Osanwe-kenta that sanwe was an inherent ability and did not need the use of any form of recognisable language, and that language only grew up as people found they did not need to use sanwe through proximity.

Hm.. I don't know. I know of no referrence about children using thought transmission - they would need will and also have what to transmit. If they haven't been already properly taught about notions and all, I guess they could only transmit, in extreme circumstances, only basic feelings. Though you may be right.

I get the feeling it is not something the Ainur were accustomed to using

I wouldn't say so; in Quendi and Eldar, it is said that Lambe Valarinwe, the language of the valar, is mentioned in the old lore of the early days of the eldar in Aman. Furthermore, in the comentary on chapter 3, Of the coming of the elves, Later Quenta Silmarillion, HoME X, it is stated that Orome "'taught [the elves] the language of the gods, from whence afterwards they made the fair Elvish speech". More specifically, in Quendi and Eldar, it is stated that:

Originally Posted by Notes on "The language of the valar", HoME XI

In such [bodily] forms [the valar] would take on all the characters of the Incarnates that were due to the co-operation of hroa with indwelling fea, for otherwise the assumption of these forms would have been needless, and they arrayed themselves in this manner long before they had any cause to appear before us visibly. Since, then, the making of a lambe is the chief character of an Incarnate, the Valar, having arrayed them in this manner, would inevitably during their long sojourn in Arda have made a lambe for themselves.

Edit:
Some more notes I made on the issue of indestructibility of the fea:

Originally Posted by Atrabeth Finrod ah Andreth

The fea is indestructible, a unique identity which cannot be disintegrated or absorbed into any other identity.

Originally Posted by Myths Transformed

...no fea can be annihilated, reduced to zero or not-existing

Originally Posted by Later Quenta Silmarillion

...the fea cannot be broken or disintegrated by any violence from without