There are some on this board who will insist you need a modified F-450 dually diesel to safely tow your kids wagon to the local park. Im not one of them...
Our F-250 gasser crew cab has slightly less HP than your 6.0 but the same torque and it does an admirable job of pulling our loaded Outback 31RQS (a little over 9000 lbs without water) on reasonably flat land, but the Outback is pretty aerodynamic as trailers go. Add a lot of water and it becomes very lethargic. The truck alone is about 1000 lbs heavier than yours. I don't think you'll have an issue with the tongue weight on most bumper pulls with your truck but the added height of a similar weight 5th wheel might be a tough pull for your engine if you want to run down the interstate at 70 mph. On flat land and secondary roads where you don't have to keep up / merge with a lot of traffic i think you'll be fine if you keep the weight below 9500 lbs or so. You'll probably lose a couple mpg with a 5er too but i don't know of many people who buy one to leave it sitting in the driveway.
