Since I originally posted the question, I did more research on the web and solved the oil capacity question. The oil capacity is 5.8 liters or 6.1 U.S. quarts.
I did the initial oil change and checked the oil level via the I-Drive. Oil level was dead on.
Where did I find this information? A web site called Automobile-Catalog.com. Look for the link to "Specifications", then search for the car in question.
The 2013 BMW X3 is not listed on the site. However, knowing that the N20 engine is also in the X1, F30 and F10 models, I looked up the specs for those cars and that's where I discovered the information.
The torque spec for the oil drain plug is still a mystery. I just "guessed" that the torque would be the same as the oil filter housing (25 N-m or 18 ft/lbs). So far no leaks.