My "average" mpg usually shows like 17.9. I reset that about 3k miles ago and it has steadily held around 18.3. The best Ive gotten was a trip to Florida (longest distance I've travelled thus far) and I think it was right at 22. I'll be doing a long road trip in a few months so I will have a more accurate reading.
As far as break in, I did several rounds of 0-100 mph pulls from 9-14 miles on the odometer. Then drove 470 miles home from the dealer and kept it between 80-95 the whole way. I think you're safe to get it on the interstate. I did do the first oil change at 2700 miles, 2nd at 5k, and have done oil changes every 5k since. Currently just hit 15k and did the oil change and tire rotation last night.