1.
For the accelerator, also consider a photosensor detector. Mount an led on the gas pedal. (Keep the wires clear of your feet.)
Then place the sensor to detect either led brightness, or led position. Getting consistent readings will not necessarily be easier than the potentiometer method.
Then there is the problem of unpredictable light levels where the pedals are.
2.
Brake pressure will not be easy to detect. The pedal moves in a small range between low pressure and high pressure.
It might work to put a pressure sensor on top of the pedal, to detect how hard your foot is pressing. However your foot must always make uniform contact with the pressure sensor each time, which cannot be guaranteed.
As mentioned already, it's vital not to attach your device so it interferes with brake operation.
3.
As to the clutch, do you want to detect clutch slippage? The straightforward way is to detect shaft rpm before the clutch, and compare it to shaft rpm after it. This may be possible to do electronically.
Or it may be easier to detect pedal position. However you must position your sensor at just the point where you notice clutch action taking place. And you must detect the range of pedal motion (say 1/4 to 1 inch), and turn it into a variable voltage. This might be by light sensing, since a 1/8 inch wide sensor could be illuminated by an led attached to the pedal, and pick up the range of pedal movement.