The Vin can take something between 6V-20V.
Yes it is but not once you have fried it.
I presume this happened because the voltage regulator inside the Arduino did not drop the voltage to 3.3V. The 3.3V was feeding my bluetooth module then.
That seems very unlikely I am tempted to say impossible. Did you have any 5V signals connected to your bluetooth module?
What a current limit knob does on the power supply is to turn down the voltage until the set current is reached. Any attempt to turn up the voltage will be over ridden. Having that knob up to full can not damage anything. It could negate any protection that current limit offers but in itself it does not damage anything.