I’m using an RPI0W. Soldered a header on for the GPIO. This is my second one. We had a lightning strike on a neighbor’s tree across the street that took out one of the relays on the relay board and as well as giving me a baked Raspberry Pi! I use the +5 from the pi to drive the relay coils and the +3.3 to drive the opto isolators. Don’t believe that an external 5V would have saved the Pi though because they still share a common ground. Pi0W is only $10US if you shop around, though.