Yes, please do. I'd suggest you use Dwarves as the east-coast types, Goblins as the western Spanish, Kobolds as aztec/mexicans and Elves as Native Americans. Also, maybe the mod should be a bit more focused on above-ground building, so..more cactus/tree diversity? And get rid of the chasm-monsters and stuff?
That all sounds pretty much what I was going to do, though I was actually just going to rename the chasm-monster 'varmints'.
Also, does anyone know if you can force a civ to use stone weaponry?
I'd call vermin varmints... speaking of which, we ought to add something there, though the only thing I can think of is yellow-belly marmots.
As far as constraining to stone, I really doubt it. I assume you ask because seeing a kobold running around with bismuth bronze macahuitls is just silly? You might want to consider giving them the elven wood-only thing. I don't know, though.
I dislike how gun/bullet modding is in DF
Now if we had a plain Native American mod, with many different tribes and all leather-type armor... that would be amazing.
Nerf farming/agriculture and make animals give more meat so more people would have gangs of hunters/rangers...
That wouldn't be hard to do. If you like, I can make the kobolds/feral elves in this mod controllable and engineer them to behave as your post suggests.
Kobolds running off with some of your cattle does seem like a good dynamic. There's no real way to get cattle to be moved by cowfolks properly, though, and stealing a live cow just wouldn't work.