Which PO type to create?

Hi all,

Facts:

1. We are on Oracle R12 (12.0.x) version.
2. We have Encumbrance Accouting setup in place.
3. Our Financial Year (Fiscal year) starts from September till August of next year.
4. The end users create Requisitions, encumber money and go through the approval workflow.
5. Once the Requisition is approved, we have few Buyers in the Purchasing department who create those Requisitions to POs.
6. Each department has their responsibility and the security is based on the GL security rule, as to which department can see the accounts.
7. There is only one pre-paid account and it is not accessible to individual departments, it is accessible only to the Purchasing/AP/Accounting departments.