Trying to get up to speed with K2 working with Sharepoint 2013. I been trying to do many things to quick prototype and learn tons along the way.
If you create a custom list, then create a K2 Application and start adding columns for your application, you can create references like choice in Sharepoint , those will become SMO's in K2. Please beware if you have linked lists within Sharepoint and later run the update for the K2 Application is conceivable that some of the lists will referente in the dropdown to the other List to the Field ContentType.
Dino.