How do you message/email the purchaser an order update?
Since Drupal Commerce is based on the Rules module, you can simple create a custom rule which watches order status and react when one is changed.

Assuming you have Rules UI enabled you can go to: admin/config/workflow/rules/reaction/import

Here is a simple Rule which you can import:

{"rules_admin_order_update" : {
    "LABEL" : "Admin order update",
    "PLUGIN" : "reaction rule",
    "OWNER" : "rules",
    "REQUIRES" : [ "rules", "entity" ],
    "ON" : { "commerce_order_update" : [] },
    "IF" : [
      { "NOT data_is" : {
          "data" : [ "commerce-order:status" ],
          "value" : [ "commerce-order-unchanged:status" ]
        }
      }
    ],
    "DO" : [
      { "mail" : {
          "to" : "admin@domain.dk",
          "subject" : "Update",
          "message" : "The order changed to [commerce-order:status-title]."
        }
      }
    ]
  }
}


You can then change the add more info, change parameters etc.

Hope this can get you going. :)