just my ideas:
Even after you have selected you drivers, you want to train them:
- Make them fit: If thay lack the strength to complete a hot (32 C) endurance their lap times will suffer.
- Make sure thay are always available to train. It's a big plus to have last year(s) car(s) available for training.
- Make sure your Skidpad/Acceleration drivers are also able to compete in an endurance as they have trained in the car and can be your backup drivers for the endurance/AutoX.
It's not easy being a driver. When the car breaks (it will) they might feel responsible but usually are not and this might effect their driving skill.