Hello,
Welcome to Teltonika Community Forum 
Question#1: How can I detect using a GH5200 or FMCXXX tracking device all these 20 units and having all the readings of all possible sensors? What are the correct Bluetooth settings and IO table preset?
- On the FMCXXX/GH5200 devices we have an option to connect multiple Eye Sensors more than 4 however parsing the data from the device might be challenging. You may refer to the links below to learn more about the parsing of records.
Eye Sensor Parsing Data: EYE SENSOR / BTSMP1 - Wiki Knowledge Base | Teltonika GPS
Question#2 : I cannot pair each time that a truck leaves factory with a preset pair of boxes. Operation is a chaos and the boxes assignation is random. Is there a possible configuration that the installed FM device or GH5200 can read ANY eye sensor and still read roll&pitch values and be able to send to my server?
- We have functionality to capture the Eye Sensor data through Beacon List where the sensors would be detected with additional information as required to be sent by the sensor. Still, you need to do some workaround on your Server end to receive the data from the sensor.
Advanced Beacon Capturing Configuration: Advanced Beacon Capturing Configuration - Wiki Knowledge Base | Teltonika GPS
I hope this helps.
Best regards,
Patrick