The oil light on the instrument cluster is an oil level indicator; when on, it says the oil level is low. It is also a sensor that tells you the level of the oil without opening the hood. The car must be turned off for at least five minutes and parked on level ground. when the ignition switch is turned to the on position in the trip odometer window you will see an oil icon and a clock, pressing the **** to the left of the speedometer quickly twice will bring up a message telling you the amount of oil; OK, Hi or -1.0 , -1.5 , -2.0. You can check that info against the deep stick.

As far as leaving that protective plate off at the crank sensor it is no problem. I've been driving mine without the plate for 15 years. Hope you used a Bosch CPS as others have gone bad quickly. Bosch is the only acceptable replacement.

Using the dip stick oil should show to the top; Half way on the dip stick is already a bit low.

PS the owners manual is available for download on this forum. See the documentation thread.