Sauron's Hroa

[Kuruharan]

I don't know if he could still shape shift. I would personally guess not. Morgoth eventually lost the ability to shape shift. I think that Sauron probably did too. Being trapped in one form at a time would be the result of the Downfall of Numenor.

And when that happened...what? He lost another body, or was he a wraith even then?

Sauron wasn't ever a wraith because he was not a being that was naturally incarnate. He did not die and then have his spirit trapped in his body by some outside force. His spirit resided in his body of its own will, with ever growing limitations.

And where does he get these bodies? Doe he create them, or does he possess a body when it's necessary.

He makes them.

And when the Ring was cast into the fire, what happened then, was his spirit completely destroyed and dispersed?

His body was probably destroyed and his spirit dispersed. It's not possible for anything other than Eru's direct intervention to destroy a spirit.