Security Upgrade from 4.6C to ECC 6.0

We upgrade from 4.6C to ECC 6.0.

In the past we use SU24 to maintain authorization check.

Do I need to run the Step 1 in SU25? (initially filling customer tables)

Does this step overwrite everything by copy tables USOBT, USOBX to USOBT_C and USOBX_C ?

If I don't run this step 1, how can I get the new SAP default values from ECC 6.0?

Thanks in advance.