why do I always read about 3.3V measuring circuits and not 5V?
my dev board has a 3.3v reg, otherwise can't see that it makes a difference


a "peak detector" can be as simple as a resistor and a capacitor in parallel "smoothing" the output of the sensor, or like Jerson wrote, of the op-amp, right?
not really , it needs a rectifier too. if the wave is not symmetrical the neg and pos peaks may be needed. plus it still needs adc code to read it in anyway


Are trials and readouts on the scope the best way to go?
almost essential, especially depending on the nature of the current being monitored,
if the current is not sinusoidal and/or varies rapidly then its going to need filtering and other compensation to get any sort of reasonable calibration