Jittery Jetta Electrical Failure revised

Our VW Jetta 2000 has these problems:

1. Slow initial start in the morning.

2. Dashboard lights up (ABS, Brakes), a beeping sound comes on (not the horn), and car sometimes turns itself OFF while idling at a stop sign or stoplight.

3. Radio turns back on even when keys are out of ignition.

4. Panic alarm goes off when you open the door from the inside.

Can someone please help? We’ve brought our car in several times to our mechanic and the problem keeps coming back. The problem seems to be related to the oil level but we’re not sure how. Sometimes if we top off with new oil, the car behaves. Other times, the oil level is fine…not high, not low…and the car still acts us. Thanks for any advice!