Estalia, for the most part, is a Mirror image of Spain after the reconquista. Lots of Local and forgen hands trying to play parts in the Kingdoms of Spain.
So, in classic Warhammer Tradition, I would just recommend taking the provinces of the time and altering them slightly.
Example, I always play my guys off the idea of Merc' Soldiers from the Northern province of Cantabaria(Almost Mirror of the real province). In my story they are an Independent province who fight and squabble with their neighbors, doing trade with the Bretonnian's of the North as well as distant trade with the Arabs and Empire. Commonly, when a Tilean Lord has the money to throw around, the Estalians will sell themselves out.
In real history They held their independence through the middle ages, fighting both fellow Christians and Muslim invasion. It was until they joined King Alfonso II that joined a "kingdom" Even then they were a "Dutchy"
Spanish History is very interesting to me, at times it reminds me of the waring states period of China. Alot of self-proclaimed kinds of Iberia all fighting over control.