The introduction of surnames in Serbia started after Napoleon just as in the rest of Europe.
I think you are making this more complicated then it actually is. Jugoslava already pointed out the geographic connection to a surname. You mention the Morava river (which is a Celtic name), but have you checked the Moravia region? These two are not related. Moravia knows a small an ethnic group called Moravians, and they were expelled. Also a lot of troops were recruited from that region in the 15th century to fight against the Ottomans which would explain why the name showed up in the ranks down south. Not all Tefter records can be found in Eastern Europe, a lot of them are also in Istanbul. As for Serbian Orthodox and Catholic Church records. In Serbia we know a pretty strict data protection law, similar to that of Germany so a lot of information can not be found online. I can check some of the books I have in my library about Moravkovic, but my advice would be to follow the trail.
As for non-Seljuks serving the Ottoman empire, it is pretty much like today. You serve and get drafted in the territory that you live. That is why many Serbs moved to Krajina and other regions so they could contribute in liberating their homeland.
So Ill follow up on the surname thing, but you will need names, dates and places.
