Combine Databases- Behavioral Health, Primary Care, and Specialty

We currently are running our Behavioral Health Services on a separate database from our Primary Care and Specialty Care services.  I am reaching out to see if 1.) Does anyone currently have a behavioral health services on a shared database with primary care?  If so, have you faced issues with confidentiality of the BHS visits?  Any other issues in these services sharing a database?

2.)  Has anyone combined two eCW databases and are willing share their experiences and lessons learned?  About how long was the project timeline?

Thanks in advance for your feedback!