Modify existing PCB and hardware design for arduino project

Edits to an existing project with a major focus on improving reliability and intregration of hardware modules into the PCB design so that the PCB can be produced and assembled including hardware by a chip manufacturer such as JLCPCB The existing project is comprised of the following: PCB with plug in for Arduino MEGA 2560 pro mini. Master PCB: This system monitors NC inputs and displays a green LED when all is normal, should the NC signal fail, the green LED turns off and a red LED is turned on (flashing) along with a buzzer. This system monitors 16 inputs and has 16 outputs. There is a mute button which mutes the buzzer for a programmable period, should the fault remain after the set period, then the buzzer is reactivated. The master communicates with up to 20 slave systems through RS485 SLAVE: The slave systems recieve an RS485 signal from the master and mimic the output of the master. The slave has the same LED layout and has an independant mute button. The master has a GSM output as well. The system has been designed and tested and is functioning as desired. This projects scope will be adding hardware to make the system more reliable including: -Opto isolators for inputs and outputs -Solid state relays to power the LEDS (currently powered direcrly by the arduino) -Intregration of the hardware components such as the RS485 module & arduino 2560 pro mini. (This must be done so that the chips can be plugged into the PCB and are removable but not the entire board) This project will require a detailed understanding of both software and hardware components. DO NOT APPLY should you not have the required knowledge and experience.