How to show approved and pending entries on front end for approvers

Unfortunately the ability to track assignee history after an entry has moved past the step is not currently available within Gravity Flow. It is on our roadmap for development. Until that is an out-of-box feature, neither a view (GravityView) or Inbox/Status block (Gravity Flow) would be able to implement what you are aiming for without some custom code. Likely something along the lines of:

GravityView likely has an equivalent way to accomplish the last point if using it. Referring to the GFAPI docs for searching for entries will likely help in both cases for examples around the meta query.

Regards,
Jamie