Problem is, the place where you want to start is a nest of powerful nations. Lonemine and Brighthall could probably stomp the tribes without using half of their troops. It's very likely that you will never reach the lands surrounding Ligoria if you do not use a boat (I would say travelling by land would take at least one or two years, and that's without taking into account other problems - ie angry Vaduds).
Not sure about that. For one thing, we never defined how big Ztah exactly is. Secondly, we don't know how many people live in all of Ztah, and thirdly, nomads/tribes have a history of being able to destabilise empires.
Nomadic tribes, due to relying primarily on cattle and hunting, tend to have a warrior culture and a relatively small population in comparison to other areas. For instance, the Huns terrorized Western and Eastern Europe by employing skilled horse archers who used composite bows and carried up o three horses with them in combat; Not only that, the Germanic tribes and Roman Empire both far outsized the riders in numbers, but they could not hope to match them logistically due to relying primarily on infantry.
On a side note, the lack of resources means that invading Ztah would be pointlessly costly in a regions where weakening yourself may well prompt an attack by a neighbour, and the same situation which leads to the area's heavy militarization also translates to the possibility of the tribes having both enough time to unite and the opportunityto exploit its neighbour's wars to raid their holds. Of course, that only works out as far as roleplaying goes, if any of them decides to invade right away it is over, although that challenges my inner, often hidden, munchkin.