Hey there, thank you for using the forum!
I will start with the topological entity sets. It is true that you have to create a separate group of these for your mesh. In order to do so, you click on the faces of interest, and then proceed to select the ‘+’ icon next under the Geometry tree. Here I selected two random faces (they have to turn to red):
Is there something about this process that troubles you?
Also, the local element size can be vital. I used the isovolumes method to locate the bad cells with the highest values that cause divergence:
This method can be described here, under the Section 2.2:
Let me know what you think about these, so we can discuss about the rest of the project as well 
Best regards,
Fillia