Another question: Will I be permitted to use Warforged Feats from the Races of Eberron book and the Eberron Campaign book?
Sure.
Expressing interest here. And...I have the BoXM. I'm leaning towards wizard but fighter domains look interesting as well. I'll work on a character concept and post it fairly soonish. Any Earth culture analog that might help me visualize the setting? (Seems on first glance to be somewhat Spartan + Babylonian). Ah, cleric is also a possibility... You got a blurb on the pantheon you use?
I wouldn't give anything a strict comparison for culture. The culture of the Empire of Sumar is like a technologically advanced (to the age of steel) version of an early Babylonian/Mesopatamian/Greek/Roman/Indian/Persian culture. A real melting pot honestly (with all the good and bad that comes with that). But the City of Zathus is more like a long term warcamp of spartans headed by Christopher Columbus into the new world. With their backs against the ocean and only hundreds of miles of enemies in front of them.
This game is set in the second of five epochs of my homebrew campaign setting. You would have only vague ideas of the first (each is seperated by enough boom that I can run them as distinct games).
The first epoch is a world just created. Lovecraftian horrors (Titans) and the equivelent of Celestials/Demons (Inevitables) walk the earth pretty commonly. At the end of that epoch, most of them have been sealed away. Somewhat similar to the Scarred Lands if anyone is familiar with it. The only reason I mention this is because it's possible that characters may encounter remnants of this or cultures that still worship these things.
The second epoch (the one this campaign takes place during) is a world full of what is essentially points of light in a sea of the darkness. I've run this as E6 before to represent how that works out. Nations are starting to form, and different cultures are just starting to show their faces at this point. Anyone can become a hero, and magic is rare but potentially very powerful.
King Marduk is believed to be 400 years old or so at this point in the game. Governor-General Zathus died in his mid-hundreds. Rumors of heroes that carry the blood of immortals are not uncommon. So a Greek/Roman/Babylonian mythology is somewhat accurate. Gods are often much more hyborean (Conan) in that they are usually real heroes and monsters that exist or did exist in recent history. I wouldn't even rank them as demigod status though by Dieties and Demigods standards.
At this point in the setting, most divinity is still very abstract. There are a handful of ascended gods, but most are physically present in the world. It's not a set in stone path though, and not everyone that is close is going to get there (or stay for very long). So from my perspective, you can take any combination of domains that work for you.
If you find a village worshipping a really big snake, it might very well be granting their clerics spells. But not every big snake is going to do that, and it might not give the snake itself any sort of magical power.
This link has a fairly well fleshed out pantheon, so if you feel like taking one of the gods described in the historic section as your own - that fits. But it's not something hard-coded right now.
http://www.crystalkeep.com/d20/rules/DnD3.5Index-Deities.pdf