This will not answer your questions, but I want to share with you about grounding using a single ground rod.
The National Electric Code (NEC), requires that if the grounding system consists of only a driven ground rod, that the resistance must be less than 25 ohms. If it is higher than 25 ohms (or not measured at all), then a second rod driven at least 6 feet away is required. My thought was that with rare exception, resistance would always be less than 25 ohms.
Well, I had to prove it. I was wiring a house. When I drove the ground rod, I decided to measure the resistance. I connected a 12.8 ohm water heater element (4500 watts at 240 volts) to the ground rod on one side and to 120 volts on the other side. My ammeter showed just 0.2 amps. E=IR. 120=(0.2)xR. (R=12.8+resistance of ground rod) R=600. Ground rod resistance = 587.2. Or 600 ohms in round numbers.
What a surprise. The ground was red clay. Gutters were not yet installed so the roof run off kept the ground plenty wet. I did not go back and measured the ohms to ground after driving the second rod.
All that is to say for your case that a driven ground may, but is not likely to achieve near zero ohms to true “ground potential”. You would need to take a wire from your panel’s neutral/ground bar to the driven rod and measure the resistance between them. You might be surprised with your “ground rod”.
If your home has metal plumbing which it sounds like you do, it is required to be bonded to the service panel. If the water supply line coming in is metal, the electrical service is required to be connected to the plumbing within 5 feet of the supply line entrance point. This then becomes a part of the grounding system.