Arduino - Raspberry Pi serial communication
You CAN NOT reliably power any model Pi from the Arduino 5V output.
You can interconnect the Arduino serial to the Pi using a voltage divider or (preferably) a level converter, as suggested in the linked article. (I might add that the linked article contains a number of errors which will not work on recent Pi models).


Better still you can use a USB connection, to provide serial communication to the Arduino, AND you can power the Arduino from the Pi (I often do this).