This sounds amazing. This has always been one of my absolute favorite periods of history (actually I'm taking a class on the artistic styles of the Mediterranean in Late Antiquity to the Islamic Conquests this coming semester, pretty hype), and I'm glad to see that it's being covered in an NRP. 

I have no clue where to even begin in terms of making an NS or characters but I love the concept. 

Actually, on second thought, playing a character in pre-Islamic Persia would be amazing, as would a Cuman or some of the steppe peoples. Zoroastrianism, Manicheanism, Tengriism, oh my! Persia will always be my favorite forever and always.