I'm heading out on vacation for three weeks but if this is still here when I get back I'll be pleased.
I do have two suggestions though:
1.) Establish the limitations of magic before characters start being created. Make certain that those limitations insure pistols and lever action rifles are still relevant.
2.) Don't bother with Texas. Have fun with altering the existing stereotypes to fit your vision. For example, maybe the orcs were defeated by the combined races and now are subjugated and work corn fields and sugar plantations. Maybe various factions are pro or anti-emancipation. It's up to you. Have fun with it!
I think it will, I mean I may make this RP a long term one once it gets started. I need to think of a big plot though, but I'm going to see if I can whip this one up really good.
1).Right, I may make you able to enchant a gun, but maybe this is hard to do for some reason. Still, you need to know how to use a gun to fire one with specialized ammunition anyways. I may make it where you can only enchant a gun to alter it's properties, but not making it hit every time or make ammunition pop out of thin air. Perhaps something elemental with guns, or you have to use certain inscribed weaponry for certain types of ammunition. Magic will be an "old art" or something that probably has always been used in one form or another, but the gun is high tech and basically an equalizer. You can kill a mage or whoever with a gun easily, they just can do a lot if they know how to use them and know how to use magic themselves.
2). I could do that, maybe Orcs were semi reasonable and basically what would be "African American" in this universe. Like, the orcs could have quite a lot of legitimacy and not be "WAAAAAGH!" Warhammer like. (Like Skryim basically), heck we could say the Confederates were half vampires, or even dark elves. Native Americans could be something like wood elves as well. I was going to go with "humans with magic fighting other humans with magic", but actually having fantasy races be a part of a historical event would be interesting. (If people actually like that idea.) It could be in parts of the south, new Mexico, or maybe even in Nevada as well. Still, it would defiantly be the cowboy era going strong and the United States is going at it with Manifest Destiny.
(By the way to anyone who may get offended, I'm from Georgia so "vampire Confederates" or "Dark Elf Confederates" would be a funny take on the Civil War. Of course, this is all in the brainstorming phase currently.) )