When is your Go-Live date?
Will you have PA-OM integration?
It would be best if your PA data prior to April 2013 would be mapped to OM, even if it's only a "shadow" of what it will be in April 2013, since the employee will require a Position that is related to a Job Key and an Org.Unit.
Message was edited by: Rémi Corriveau P.S. : After loading the OM data in April 2013, you'll should execute an Action to reassign the employees to their proper Work Place Basic Pay (Position/Work Schedule Rule/Salary Grid, etc.) and Payroll Accounting Areas.