It sounds like you are setting yours up just like I did mine. I have the switch just under the dash so when I work on the car with the key on I can shut the buzzer off. I used a delay on make timer from Amperite 12D2-20SST1A. It was about $30 and I had them throw in three resistors that were a dollar each for an option of a 2, 3 or 4 second delay. The resistors were .25 watt, 100K, 150K and 200K. So normally when I get in and start it I will not hear the buzzer. The resistor just plugs between two terminals on the timer to change the delay. I have the 2 second resistor in now. You can add an adjustable resistor if you want.
I have a regular
oil sender for my gauge and also an idiot light sender that grounds with less than I believe 8 lbs. of pressure. I also added an
oil warning red light. I put it next to the
oil gauge. It just uses the Acc. power with the key on and ties to the same wire that goes to the sender for ground.
Gunner is right you can do it cheaper if you build your own timer, but it wasn't worth it for me. To much other work to do and not enough experience with that.
Wayne