You'll love the truck. Mine's a year older, tricked out with the Max tow and the HD Payload package. That said, average around town is about 17.5 to 18.5. Winter daily driving dropped it to 15 to 16 (due to prolonged warm up times in our frozen climate). Highway around 20. Yours probably will be better as I have the high gear transmission.
Towing the 8,000lb fifth wheel it runs about 10.5. The 3500 lb boat, around 16.5. I can easily pass semi's going up a 6% grade with the 5th.
I've found going up to premium doesn't quite get the 10% increase in milage the manual suggests. That said, if the price of premium is less than 10% of regular, and looks to be steady for a while, I'll move up. Will also use it when towing on longer trips, just to get the increase in mileage between fill ups.
2012 Ford F-150 Eco, Max/Max
Jayco 26.5 RLS, Reese Sidewinder