who wouldn't?

What is the difference between the Gain and the Output?

Gain = The amount of "boost" applied to the microphone's signal via the preamp circuit.

Output = The volume of the output circuit going to the next piece of gear in your signal chain.

What does the Impedance button do?

It changes the impedance at the preamp circuit - affecting microphone gain, tone, and noise floor. It's a little difficult to put this in layman's terms (envision a garden hose...)
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...And Limit:

Limiting sets a "ceiling" or maximum volume on the signal - anything beyond the ceiling is gained down to the same relative level.

And Phase invert:

It affects the signal (which is an alternating current or "wave") by taking the positive half and flipping it to negative and vice-versa. Useful in avoiding (or creating) the following:
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If it's a tube I'm assuming having high gain and low output will soak the signal in tubeness; low gain high output will leave it nearer untouched.

High gain and output is asking for trouble.