The pilot reported that he did not have the airplane configured properly for takeoff. During the takeoff roll from a field, he took his hand off the throttle to extend a notch of flaps. The throttle lever subsequently moved out and power was reduced. The pilot did not recognize the power reduction, or that the elevator trim was set to a nose down attitude before the airplane traveled off the runway, down an embankment, nosed over, and came to rest inverted. The airplane sustained substantial damage to both wings and the rudder. The pilot reported no mechanical failures or malfunctions that would have precluded normal operations.