The stupid are sat my side of the screen. Frankly it's all guess work until I build the thing with the appropriate amplification. I wish I wish I wish that I could calculate the gain of the two pentode stages in my schematic. It's to do with the plate /cathode resistors ratio I think.
One way to ball park the possible entropy rate is this:-
On the Arduino, sample 8 bits @ 10KHz. I like 8 bit samples because they look like bytes.
Assume the input signal level to the ADC pin is 50% of full range. That's effectively 7 bits /sample.
You'll have to take my word for it that a sampled white noise signal contains about 25% entropy.
So entropy potential = 10,000 * 7 * 0.25 = 17500 bit/s.
That's a bit kinda like 24kbit/s. Remember that this is pure entropy (randomness) not sampled data. The 25% compression factor means that this stream will pass the standard tests for randomness. I hope.