Precautions to be taken during PS implementation from FICO angle_Reg

We are in ECC6.0 Already FICO,MM,SD & HR are implemented. So naturally in Controlling we went for Cost Center Accounting and there are about 5,000 cost centers. Now we are going to implement PS. What are the precautions to be taken from FI side and from CO ange? In case of PS there will be WBS elements then what about these cost centers in CO and in HR. I am new to PS. Please clarify.