Hi gprocher,
Thanks for reaching out to us with this.
As a rule of thumb, we suggest that each unique ABN have their own separate QuickBooks file.
This is due to the way that QuickBooks intertwines with different sections of the platform and it can be a difficult task to separate data from two different businesses.
Having a unique file for each separate business ensures that there is no data cross-contamination.
The same goes for personal and business finances.
Let me know if you needed any further clarification.
Kristian.