Hi @omer_1 -
To support your pressure sensor, you’ll need to get ArduSub to understand how to talk to it. This would typically require modifying the source code of ArduSub, compiling it, and flashing your custom version. An RS485 to I2c converter is not likely to help you much in this pursuit - a BluART would let you connect your sensor to the system and handle the data from there! Others on the forum have discussed this before.
QGroundControl is just a ground control station, displaying what the vehicle is doing. Your second approach, controlling your vehicle from a script, can conflict with QGC’s own control link if you try and do both at the same time!