Interesting question! The main reason that there isn't much information is due to the lack of primary sources. The reason being: the Seleucids wrote everything on clay tablets, in contrast to other civilizations in the geographical region that used papyrus, resulting in the clay tablets being pretty useless due to the tablets growing brittle with age and deteriorating due to the climate of the area. Furthermore, certain things that are known include governmental structure due to outside observation; for instance, we know they were a satrapal society much like Persia, but besides that, there really isn't much out there in terms of primary sources regarding things like administration, economic practice, and much, much more, unfortunately. Regardless, my personal favorite book on the Seleucids, and arguably one of the most extensive on the topic, is From Samarkhand to Sardis: A New Approach to the Seleucid Empire.

Please feel free to reply or PM if you have any further questions regarding the matter.