I have ordered the starter kit and plan to build an ammeter that measures 0-650A (it's an EV!).  What it's actually measuring is a small voltage (750 mV = 500 Amps) across a shunt resistor at the negative end of the high voltage loop of the car.  I will use a DC:DC converter/isolator to eliminate ground problems (12V system is grounded to the chassis but the 120VDC system is not, it is floating).  First stage of my ammeter will be an op amp diff amp (high impedance) that simply measures the difference between voltages of the two terminals of the shunt resistor.  That will be followed by a precision absolute value (full wave rectifier) op amp circuit that will allow me to measure propulsion current as well as regenerative braking current (flows in opposite direction to charge batteries while braking).  My question:  to power the Arduino board and its shields, do I need to provide 3.3V or 5 V, and how well regulated does Vcc have to be?  I'm sure my newness to this shows in the ignorance of my question, but I'd really appreciate some help from some of the more experienced members.

I got no responses to this in about 10 days, so I thought I'd share what I found out separately.  The Tiny Duino has no voltage regulator on board so I will have to provide one externally.  It needs Vcc voltage between about 3.0 to 5.5 V DC.