Gyro + Weight indicater to arduino using RS232

Hello all, I recently started a project where I have a scale for on a boat to measure the weight of fish, since the boat moves left and right the weight will go up and down since the fish will go to the sides of the scale. Unfortunately it isnt possible to let the scale move with the movement of the boat so I am adding a Gyro on the scale ( the 9DoF Razor IMU M0), for the scale I already got a controlbox with a panel on it what indicates what the weight is of the fish on the scale (This panel: MCT 1302).

So my goal is to have the data of the MCT 1302 (the measured weight by the scale) going to the arduino using RS232 and also getting the data from the Gyro (The 9DoF Razor IMU) all connected to the arduino by also using RS232.

One problem is, I havent used RS232 much and cant find the right answer to my question anywhere so my question is: what ports do I need to use of the MCT 1302 going to the arduino and which ports I need to use from the Gyro (9DoF Razor IMU) to the Arduino and where on the arduino I need to connect this all..

if needed I do got a MAX3232.

Thanks in advance.

You'd want to use a processor with multiple Hardware Serial ports (don't bother with Software Serial) such as a Mega, Teensy, Feather M0, etc. Yes, if your instruments are true RS232, you'll need to translate to logic levels with something like a MAX3232. Power that at the same voltage as your processor's logic levels (3.3 or 5V).