1. Why the fuck is Xerxes a giant, flamboyant drag queen?
No fucking clue, have been trying to figure that out myself for some time now.
2. Why does Xerxes army contain mutant, non-human things?
I think they were trying to make some bizarre suggestion that Persians took the Spartan's rejects and made them into soldiers, however, not all of Sparta's rejects were mutated. I think that was just over exaggerated because someone thought they'd try to make a giant point out of Sparta's obsession with perfection and ended up looking like a moron instead.
3. Why do the Greeks and Persians all speak English?
Because the Americans are too stupid to read subtitles anymore.
4. Why are so many of the Persians so heavily pierced?
Hmm... You know, I know I'm walking on a really sharp razor edge hear not finding the exact quote and reference for you, but without doing any googling of any sort and having to dig up deeply repressed memories of Sunday school (gag me), I seem to recall some reference to Persians being totally profane and vulgar jackasses. I think this might have been the author's way of protraying that. Then again, he could just be a total moron. After all, I cannot recall one single mention of Xerxes even being unusually tall and the man clearly loved banging women from what I understand so I doubt he was a drag queen either.
Maybe the author/writers were just racist.