which is the real aspect of the time god auriel,akatosh,alkosh,alduin, or even tosh raka? If none of them are the true aspect of the time god which is the closest to the original.

The closest aspect to the original would probably be Bormahu, the aspect the dragons themselves formally recognize. There's no real "true" aspect anymore because the Aedra are "dead."

To give the dragon a name is to limit him. There is no 'true' face, for to recognize his face you must separate the face from the truth.

Pretty much this.

Although I do think it's a possibility that Auriel, Alkosh etc merged with Aka/time itself in one way or another when they ascended.

How many aspects are there now?

Not too sure tbh. There are three at the very, very least that I know of. Could Ysmir be considered an aspect?
I remember dialogue in Oblivion. When you were in Bruma they'd sometimes say 'the nords prefer their dragon Ysmir to Akatosh' (something along those lines).