Super basic Q: How to regulate voltage in this basic circuit to avoid damaging the heating plate?
Go back on amazon and look for 5V buck-regulators... One like this one will do.

Hook the IN side to the generator and the 5V side to the heater through a switch You will need
a voltmeter to adjust the output to 5V one time. Adding an LED with a 330R resistor in series with it , in parallel with the heater would also be a nice feature. You should also add a diode before the regulator to protect it when you crank the generator the wrong way.



simulate this circuit &ndash; Schematic created using CircuitLab

Problem 2: The device is intended to be hand-held and mobile, and thus sometimes not grounded during power generation. Is it necessary to ground it to prevent charge build-up (and shock to someone handling it)? If so, how?

Well the only charge buildup that may happen is if the crank mechanism builds up static electricity. Otherwise the voltage you get will be whatever the generator creates when you crank it. So grounding is not required.