Use Arduino Pro Mini instead of Arduino Nano.

• This solves the problem with communication to the A6 module at 115200 baud. The Pro Mini does not have anything connected to the hardware TX/RX pins, this means that there is no need to use any complex code for the serial interface to the A6 module.
• The Pro Mini is much smaller than the Nano. Therefore the Pro Mini could probably fit under the A6 module, reducing the size of the PCB.

Use a relay board to drive the external lines.

• This eliminates the need for transistors, resistors, capacitors, and terminals.
• This allows connection to multiple types of external equipment, for example directly to a remote control fob.