Most is from JSTOR.

Here is a tidbit on Seleukos I. Also on the following page.
http://www.ancientlibrary.com/smith-bio/3105.html

Remember that the description on him as a god is written from a Seleukid viewpoint, ie propaganda.

Marduk is a Babylonian god. We were limited by 6 gods so we took some important ones and some to distinguish them from other factions. However, it's fairly sure to assume that the Seleukid empire had a massive amount of gods.