Having a surface or scan of the last is essential to creating a CAD model for 3D printing the heel.
That being said in order to create a good heel, experience is required to get thru it in a timely manner.
I have developed several rules for creating a good surface that will fit well, translate into 3d printer, and be completed as quickly as possible.
Because 3D printing allows for intricate parts that would be nearly impossible and certainly to costly to machine it is the only way to go.
I always look for the best way to manage the Heel breast; usually a second part that is wrapped independent of the back half and attached with a screw to ensure a tight fit.
When working with the Stiletto you must add a steel rod or tube. For the printed heel I leave a hole from top to bottom (make it about 0.005" larger all around) then you usually have to use a drill to clear it out and then epoxy the post in.