I think that with the nature of time being cyclical, the use of the terms 1st, 2nd or some other number in a sequential order largely becomes redundant and meaningless. For example, if you lived in the Third Age, the age coming before your ancestral memory before the First Age is forgotten, so that putting them in order is largely dependent on where you exist in relation to prior ages.

I think the world will be pretty well set up at the end of TG. I think the evil of Shayol Ghul will either become the next ultimate evil or be instrumental in destroying absolute evil, leaving the world in the hands of the petty disagreements between mortal beings concepts of good and evil instead of god-like embodiments of those forces.