Writing an epic fantasy story, need help.

Hello there

I'm basing one of my races on the Achemanid Persians/Sassaind Persians.

I would like help on what was their daily life style like? What sort of architecture did they create? Is it possible to add in Jassnaires and make them a totally different fantasy style unit?

I want to know:

What the formations and the organisation of the administration of both empires was.
What their armies contained.
What I could create out of this.

Etc.

Religion based - I believe its Zorostranism. I wonder if I could make up some fantasy religion?

Thanks

Writing an epic fantasy story, need help.