Yes : )
1- petrol in liter, the actual fuel remaining. The most difficult feature to add. The stock sensor gives rough indication due to sensor limitations and tank shape, so difficult to get fuel in liter from this sensor.
Or you are talking about liters you filled from filling station?
2-Yes, can be added, rad fan indication when they turns ON and OFF.
3- If 1 possible then only this can be added.
regards