Hello Franz!

@You : "...I may just need to understand what is really important when using SubD...."

Simple....two things :

1) Create only quad polygons and a very few triangles. No polygons that has more than 4 edges if you really want good results.
Ok, if you know that some particular area of the object will not be framed by the camera then you can do what you for with that area,
but if something has to be viewed by the camera and/or close to it you must have quads if you want good results when subdiv.

2) Create edge loops only where you need it.

But these two points are not simple. You need years of experience :)

Ciao!

Marco (mkdm)