Serbia was called Rashka at that time, it was beginning to be called Serbia in the 12th century AD and later. My sources do not mention the capital, although I would recommend using Doclea, located in Montenegro, as Rashka was under Zetan (the name of the country at that time) control.

Like I said earlier, the Croatian capital would be Klis (the traditional seat of the dukes in the 8th and 9th century), immediately north of Spalato. If you used Zara, the province would have to be Byzantine, as Zara was a Byzantine city.