make a volt, amp and wattage meter.
The Arduino 8-bit UC's like the 32U4 and the 328 have a single 10-bit A/D but have multiple channels to the successive approximation unit. So, the voltage readings will be a numeric value of 0-1023.
The issue you will need to consider is that the A/D unit needs a reference voltage which can be no higher than the uC Vcc... Typically 3.3V or 5.0V but one can use an precision (separate) analog reference source. For voltages higher than Vcc, a precision resistor network can be constructed. The input impedance presented to the A/D should be approximately 10K.
There are a number of inexpensive current shunts available, the most interesting are the active Hall effect units. You must carefully match the sensor to your specific ranges of need.
Good luck,
Ray