Shayera Thal was named after Shiera Sanders.In Post-Crisis comics, it was hinted that Katar Hol was named after Carter Hall. Makes sense, since his father Paran Katar knew him on Earth. So its possible that Paran was close friends with Shayera Thal's parents, and named their daughter after Carter's wife Shiera.
The answer to all of the questions regarding Hawkman's origin story is all of the above.He's an alien that has the reincarnated soul of the terran Egyptian pharaoh. The Thanagarians used to have a relationship with the primitive humans similar to that of the Go'uld from Stargate SG-1 and all the magic parts of his origin are really just sufficiently advanced technology.
Hawkman and all the other Thanagarian exiles on Earth will form their own country.And what will it be called? ...Hawkmanistan.
The origin of Nth metal in Earth-2.Both the pre-Crisis Earth-Two and post-IC Earth-2 Carter Hall created or discovered Nth metal on his own, since Paran Katar (and Thanagar) doesn't seem to exist in those universes. Though, in ancient Egypt, based on Hawkworld Annual #2, Horus the Hawkgod gave the gift of Nth metal to Prince Khufu in the form of a meteor.
Paran Katar was part of the Talon of Truth.He learned about the Hawkgod from their written documents. He borrowed or stole one of them and used it to (re)invent the Nth metal.
The DCU relaunch will bring back Katar and Shayera.Or at least restore their Silver Age history.