To answer some questions in order...

[@Polybius] - Firstly I'm thinking Oao's realm would be concurrent with the mortal realm. Her true realm doesn't lie beneath The North Crown however. It has become her unofficial home ever since the sun drove her from her true home: The darkness between the stars which she was born into long ago, nestled safe within her egg. Ever since then she has been barred from returning by the sun's light ever since, even at night due to the light reflected off the moon's surface which gives it it's characteristic silvery glow. There is only one night each month where Oao can tap into the power of her realm. That night is the night when the moon itself is at it's darkest: the night of the new moon. For the remainder of the time she remains hidden up in The North Crown.

[@Leotamer] - In terms of chronology I'm thinking the order of which gods came first should start with the gods of basic elemental forces such as earth, water, fire, darkness, light, ect. After those would probably come the gods of humanity and after them would come the young gods. Just my take on what would seem like the likeliest order of arrivals.