If you are referring to the parallel block, it will still depend on your requirement. Take note that parallel blocks are used to run multiple actions/approvals consecutively. This is usually done when you have a complex workflow with lots of steps and doesn't require on each other to complete to proceed to the next non parallel action.
To answer your other questions:
- in SharePoint Designer workflows you can add details on the history of your workflow per action so that you know what specific action was completed
- you can just create a specific view for your list/document library showing the approval status of each request so that users can see from which approver the action is still pending.
- there are multiple ways of debugging a workflow. the easy way is using the workflow history items while there is also a way of debugging them by converting them to windows workflows and running them in visual studio. it really depends on what specific debugging you want to do.