Unique Self

I'll try and give you some of my interpretations regarding the questions you ask. 

"What does Ken mean when he says that perspective is prior to material existence?  Is he speaking of the perspective of One Spirit or another perspective that arises immediately upon manifestation prior to material manifestation and long before humans?"

I don't think he's speaking of any particular perspective.  I think he means that the entirety of the manifest material world arises solely through perspective.  Any and all individuated "it/thing"s are only known and only manifest as a product of perspective.  This might be seen as excessively solipsistic, but really it's true.  Behind all of manifest creation that we are privy to is a mind or perspective that is the medium and ground for it to arise.  No one will ever find exception to this.

"Are all sentient beings unique selves or is this only reserved only for enlightened beings?"

I don't know if this is how Ken would conceptualize this, but...  I would say all sentient beings have unique selves, but recognition of one's unique self requires first direct experience or realization of reality transcendent of space, time and individuated perspective / ego self.  It's like the fish living in water.  He must first escape the water to know that he is wet.

"Is there such a thing as an enlightened being or just enlightened activity?"

What is it to "be" without entering into the manifest world of activity and cause and effect?  That is "enlightened being" and enlightened activity is the result of aligning our individuated selves with the direct realization of this "is that isn't".

Is there a such thing as a fully enlightened individuated person? No. That's simply because the ground of being, the source and sum of all creation is a transpersonal domain.  To paraphrase Ken, that I Am is the same for all of us.  It's an undifferentiated, unmanifest reality.  But, that I Am, that we all are, is always already fully enlightened.

"He seems to see the unique self as different from ego. Am I correct in this?"

I don't think so, even though he does distinguish between unique self and ego or the "egoic" label.  I think your conceptualization of it is closer to his than you thought.  I might re-frame the unique self as the re-inhabiting of ego, illumined by the direct realization of Spirit.

As an aside, I think this too could be seen as a Pre/Post confusion.  The unique self is ego, but it is not egoic.  It is firmly anchored in a trans-egoic realization.  It's the submission of one's lower self (individuated self) to one's higher self (I Am, Brahman, Emptiness, etc.).

Actually I'll go further than that.  It is the embodiment of the Non-Dual realization.  My finite, individuated, manifest self is none other than my infinite, unified, unmanifest self.  I honor their distinction, but see even that as ultimately illusory.

"Practically speaking, in my opinion, most egos will tend to grasp this teaching to inflate themselves with very negative consequences to ourselves and others."

I fear you're probably right, but Ken probably knows his audience better than I do.

I hope i've been helpful to you.  If not, at least i've been helpful to myself by clarifying some of my own thoughts.