For the record, there is no reward.
Since it is an automatic voltage regulation, as long as the output is all the way. If you need three circuits, copy three circuits in the same pattern as one.
For 3A current, switching regulator LM2576 is recommended.
Having a fixed output or an adjustable output. For details about the circuit, see DATASHEET of the device.
As for voltage and current display, it is recommended to purchase the digital display head directly.