"switching box" with microcontroller and relays
You will need to select relays appropriate for your load. A relay for microvolt signals (microphones, thermocouples, etc.) will be rather different than a relay for floodlights or electric heaters.

There MAY be some very small relays that can be driven directly from the logic output of a microcontroller IC.  But typically you will need a single transistor to switch the coil current. And a resistor to limit the transistor base current, and a diode to protect the transistor from the voltage spike from the collapsing magnetic field of the relay coil.  Like this....