The extra steps are necessary so as to have a “sprue” for the two-sided machining operation — probably they could be added to the 3D model easier.
Carbide Create Pro has 3D modeling like to that in Vectric Aspire which seems to be best suited for decorative use.
If you want something to come in at a given size you will need:
- to know what that size is — check the STL using a 3rd party tool such as Microsoft 3D Viewer
- have the STL saved in a file format which accurately captures that size
- import into Carbide Create Pro at scaling 1.0
- set the Height on import to match the height of the model
See:
I suspect you’d find MeshCAM a bit more workable for this: