With the Rivers, IG, I just put them in at random by way of example. There is an image of the area with rivers from one of Neon's posts which I think we're expected to follow so that the rivers are consistent from region to region - apologies if you already knew this.

Actually, by some weird coincidence, my example rivers are not far off the the ones in Neon's map.

I like the idea of organised communities of orcs/gnolls/goblins etc fighting each other.