I think the diode part can be compensated by calibrating the circuit. Im going to have a variable resistor that can move the output in the range of 3-7V, then i will use the computer calibrating part (either the chip of a furmula on the final result) as a kind of fine tuning.

Just thinking about calibration. Whats the best way? I was thinking to connect up my multimeter, apply different loads and match the output to the multimeters output. Would that work well enough?

How do you choose a capacitor and bleed resistor? I know you sort of told me but im not sure. Which do you pick first? The capacitor or the resistor?