How will I maintain a hierarchical structure in civicrm?
CiviCRM is pretty egalitarian - they are all just Individuals.  

There are various ways you could model this which depends to some extent on what you want to do based on that data.

One option is Relationships - eg create a Manager/Managee relationship and create relationships for all the places where you have lines.  If you want to record a level in the hierarchy you could use a custom field.

If you want to use those relationships to control access (so that eg Line Manager1 can see only P1, P2, P3) then have a look at the Relationship Permissions ACL extension