architecture - Need guidance on inventory application design -

currently i'm working on inventory management application (later on can integrated accounting application too), , need in deciding 1 of important system design related decision on following:

requirements:

1. factories having multiple accounting firm (company), , goods come , go these multiple accounting firm, physically consumed in 1 factory , production being managed single manufacturing unit. there no separation of physical stock or produced items based on accounting firm. again goods sold different accounting firm.
2. inventory data, sales & purchase given company wise
3. no production related records being managed separately
4. inventory , production data managed in single application companies (accounting firms) unified, customer can have reliable tracking of stock/inventory items

now, want suggest on following:

1. what suggest, whether keep company wise data separate db different each other
2. or store them in single db separate identifier company , have single application can access data @ same time separate reports well, may user wise access can setup?

what suggest, , right approach?

since need access of data in single application across companies best have data in same database company identifier.

in addition single database prefered due to:

• simpler maintain due, single database backup
• simpler add new companies

the case when not go single database there strict security requirements, not met single database solution.