Congrats on your new Thrustmaster T300RS! For some recommended realistic settings, you might want to check out this site: https://www.briankoponen.com/euro-truck-simulator-2-thrustmaster-tx-t300-settings/
Just a heads-up, though: any settings you apply are at your own discretion. The driver is responsible for any liabilities that may arise from their wheel settings. Always make sure you understand the regulations and drive safely! Good luck and have fun!