Offset depends on vehicle fitment. Wheel diameter depends on what you like and what tires you can get.
Just make sure if you are upsizing the tire diameter that your fifth wheel will work with the increased truck height. Also make sure the wheel weight rating is the same or greater than the stock wheels and the tires are E-range.
2011 Ford F350 CC LB DRW
2014 Eagle Premier 361REQS