Custom Employee Manager hiearchy in custom table

1) Invoice Approval workflow has to be based on  Custom  Approval employee Manager hierarchy  based on data feed of 3rd party HRMS refreshing daily in a  custom table.

      We need to read the custom table and use it as source for generating approval hierarchy. This is constantly getting updated.

                 My idea:  Create Custom Trx Type, Approver group based on query from custom table.

2)  What could be the best possible custom User Interface  design to be based  on  custom table to allow users to view the employee manager custom hierarchy. they should be able to edit the hierarchy apart from data feed.?