Hi Neeraj,
based on your diagnostics, I would recommend flows storage on separate server having a quad core CPU, 12-16 GB RAM, 900GB of space for storing your current flows for a year. Make sure to upgrade to NTA 3.10 or 3.11 before installing NTA 4.0.
(just a note here: your diags show 10k flows/s opposed to 687k you claimed, do you plan to heavily extend your current network or you made a typo?)
To query the data from new Flow Storage you can use Orion built-in reports or SWQL studio from Orion SDK (Orion SDK Information) to query raw data.