Let's see, you have the basics of a flight data recorder already...
GPS will log the flight track and total time, allowing you to calculate
average speed.
EDM-700 graphic engine monitor allows you to download the previous
flight(s) engine operation data allowing you to determine exceedences
and engine start/stops.
What are you missing"
A remotely mounted digital video recorder with audio input from the
intercom, that begins recording when the master is switched on.
What are you worried about?