As an update on the amount of oil added:
I checked and rechecked the oil level using the electrodipstick and found that it always registered full after adding 6 quarts. I would do this on my way to and from my carpool pickup point which is about 8 miles away. The weather here has been on the coolish side.
Last Fri I drove in to work (~60 miles) and checked it again. On the way home, it was showing half a quart low; the indicated level was in between the two marks displayed. I added half a quart but have not taken it for a long enough drive to note it again.
My theory is that the car was quite warm when I drained the oil, hence the cooler thermostat was open, so the oil drained out of it. By the time I added the oil back in, the thermostat had cooled off again and closed, so none of the fresh oil I added made it back to the cooler. 6 quarts made it read full therefore.
When making a long enough drive to actually open the cooler's thermostat again, a half quart flowed into the cooler, and the reading was now low. Adding the extra half quart should fill it again. We shall see.