I would argue the order should start with NUCC. I have not done a side by side comparison, but the NUCC code set has the most granular codes and includes different provider levels.
I would also like to add "clinician title or provider level or provider certification" (open to other naming conventions) to the Provider table. Values would be the concept_ids for MD, RN, CNM, EMT-I, etc. which are found in the NUCC code set.
Thoughts @aostropolets, @Christian_Reich, and all?