Hi Siva,
SAP PI/PO exposes a standard servlet MessageOverviewQueryServlet that can be used by external applications to retrieve message overview statistics equivalent to what PIMON Message Monitor Overview displays, via HTTP. You may look through blogs External Collection of Message Processing Statistics from Advanced Adapter Engine of PI/PO and Michal's PI tips: How to get RWB message overview data to an external system? that provide details about usage of this servlet. Based on list of your requirements given above, I would assume this functionality shall suit your analytics needs for the developed dashboard.
If you need to further drill down and retrieve information on specific messages, then you can get use of a standard SOAP service AdapterMessageMonitoringVi, which is described and demonstrated in the blog Reading Messages from PI System.
Regards,
Vadim