Thank you for the wonderfull answer Martin!
Currently the RaspberryPi only has the SD card as memory space indeed, but it would be possible to attach an external drive.
After creating the Modbus Server Channel, I was instantly able to view all the values that I wanted. Now I can experiment with how we want to store our data.
But first we're going to see if we can attach it to the internet so we can use the MervisDB.
Thanks for the info!