SU25 after an SAP upgrade to EHP5

We have recently upgraded from SAP ECC 6.0 to ECC 6.0 EHP5.

We are in the phase of SPAU. In that our Basis Administrator told us to perform SU25 for authorizations update.

I have gone through the documentation abt SU25 in the SAP help portals, but have not yet clearly understood it.

Can you please help me answer some queries.

1. Since we were previously using PFCG, we have to skip Step 1 (Initial Filling of Customer Tables) and directly execute Step 2a ??

2. After executing Step 2a, will the new default values deliverd by SAP be copied into the customer tables (USOBT_C & USOBX_C)  or will it only compare the SAP delivered & customer tables and not overwrite the customer tables???

3. After the Step 2a to 2c is over, do we have to execute Step 1 (Initial Filling of Customer Tables)??

4. After the customer tables are populated with the new check indicators, do we have to manually go in to each and every role & add the additional checks or will they be automatically reflected in the roles & one has to just maintain values for them??

5. Once we copy the customer tables with the new SAP delivered values, is it possible to revert back to original values???

6. Is this the correct procedure to be followed for post processing?

I am doing it for the first time, so asking in details to avoid any mistakes.

Thanks in advance.