Pixhawk on a tractor (i2c or ADC problem)

Hi all! I know the idea isn’t new and there are already some projects on youtube related to this.
I want to make one of my tractors working automatically. i already solved some stuff like autosteering and control management via the pwm ports. By now there is nothing done in the trator so no photos avaiable. but my biggest problem so far is to aquire the data from it like engine temp and oil pressure as well as gearbox position.
as far as i’m aware there is only one adc port on the pixhawk
so i thought about placing an arduino managing the data and send it to the pixhawk.
then i searched almost everywhere and i coundnt find a tutorial for this.
i have some little to small experiente with the arduino programming language.
Can anyone point me any direction to follow?