Reserved.

Maybe the old kinda monotheistic religion the Getae and Dacians worshipped, Zalmoxism, would fit well with the whole theme of the mod.

Given you mentioned Sumerian religions in the plural, I imagine you're planning on doing more than one? If that is the plan, then I'd suggest considering making the faith-divide by city-tradition. Uruk for example emphasized the worship of Inanna, Anu and Uras/Ki, and Dumuzid (though, his actual worship was more or less just an extension of the worship of Inanna...), Nippur focused on Enlil, Ninlil and their children (Ninurta, Nanna, Nergal, etc), Ur focused on Suen, Ningal and their children Utu, Inanna, and Ishkur. Noting, of course, that this was just emphasis, not an exclusion or necesarily (though, sometimes it did) lessening of other gods...though, strangely it's the Ur tradition that actually has Inanna take over the pantheon by marrying An and thereby acquiring his divine powers, and those of the rest of the pantheon.