First, congratulations on your purchase. Second, thank you very much for taking the time to share the story as well as the photos of your car.
Calculating mpg for your car using our local gas station pumps will not be very accurate. Your car may have a built-in mpg calculator. If you must rely on gas station pump, I would suggest using an accurate, graduated container to measure the litter of gasoline dispensed by the pump to see what the litter is for THAT pump. This way you can use the same pump to refill and get accurate results.