What is the best approach to updating PS when there is a mix of outsourced and inhouse benefits?

We are preparing to outsource most of our health and welfare benefits to a third party administrator but several benefits, paid time off (leave plans), savings plans, company provide life and LTD in will continued to be maintained in Peoplesoft and we are attempting to determine the best approach.

A few items to note:

There are substantial changes being made to the leave plans, we are moving from traditional sick and vacation plans to Paid Time Off (PTO) structure with tenure step-up.

Benefits administration is not pristine (multiple out of sequence, job change flags, not assigned, some OE 2020 are still open, etc.)