Help biasing Alice JFET

[Khron]

However is my signal generator output reasonable and or what would you suggest is an appropriate input range to test for?

Those mV values are not real - not unless you happened to calibrate those against an AC voltmeter. Other than that, REW should cover all your needs.

 

[abbey road d enfer]

I have tried adjusting the source resistor although the pot I have is 1M so it's not ideal using it in parallel with the source resistor to ground.

Which is not correct...

My assumption is that I'm biasing for THD+N

Correct, though it must be put in perspective with headroom. Fortunately the optima are quite close.

and it would be nice to know what is an ideal input voltage or a safe one.

Distortion increases with signal level, so using a relatively high level will improve the measurement sensitivity. Of course there is a hard limit when the output clips.
In a typical Schoeps arrangement, the maximum peak-to-peak output voltage is about one half the supply voltage (typically 6v for 12V supply). I would suggest using a signal of about 10-50% of this limit. This would bias the stage for loud SPL and eliminate noise from the measurement.