How we approached this, we have maintained four groups and finding it a clean approach
Cross-Application Components >SAP Business Partner > Number Ranges and Groupings
1) Any object created in SRM – such as Purchasing Org, Purchasing Group - Internal
2) For Vendor s – external
3) Employee CP (central person) external
4) Employee Org. External
Then we maintain number range for each groups, you can tell by looking at the number rage since you know the number ranges