You are welcome.
Military organization was very similar to Byzantine one with some Slavic traditions in early and later with some tactics of western countries. Army equipment was mostly byzantine(early era). In this early period Serbian army relied on axe, speared units and javelin throwers/archers(derived from old Slavic tactics). Heavy cav was not that strong and numerous enough to hold ground against Byzantine, Hungarian and Bulgarian, due to economical limits. Pretty much ambush tactics in hilly terrain with that combination and cavalry making surprise attacks in flanks destroyed a lot of byzantine and Bulgarian heavy cavs and infantry and held Serbia independent for many years. Nobles were most professional heavy cav and unit in Serbian army but their number made them weak compared to neighbors Pretty much you have all early cav. you are missing late ones if I remember. Pronoia cav is missing if I remember correctly. Just what is a big miss is Vlastela. they are horse archers and when they get out of ammo they pull spear. Nope. Vlastela were heavy cav(Vlastela can be translated to "Nobles") armed with one of the best weapons and armor(in early era mostly byzantine with some small elements from italians, in late era mostly italian/german style) charging wtih spear/lance+shield and in melee sword+shield. typical heavy cav. Also men-at-arms are missing if your mod goes to 1310s. But we will talk later about unit details.
Economy was random. for such small nation with small iron mines, agriculture, fish ... did not produce so strong economy. Later more lands were conquered, discovered a lot of gold,silver and some other metal resources in Kosovo and Metohija and other part of kingdom. Metallurgy developed so much which boosted up serbian army in both infantry and heavy cav + some artillery.
Society. Well speaking of religion, majority was considered Orthodox. But there were also catholic Serbs mostly around Adriatic coast and also there were Slavic Pagans who did not wanted to convert to christianity. Serbia at this time was developing as feudal state, but still people acted like tribal people. It was hard to completely unite such people. 2-3 times Serbian lands were divided into several principalities. Not until Nemanjic dynasty taken throne. I am not sure if this is what you wanted, but for M2TW I only see religion as important, correct me if I am wrong If you need more tell me and I hope this short info I posted is helpful. Also tell me when you start(if you want to start) making Serbian units. It think it is better to start sending you more detailed infos+pics than to send them right now.