Hi,
I have found that the F-150 with Ecoboost, max towing, and 3.73:1 rear axle has a maximum cargo rating around 3,000 pounds. This is almost as much as the F-250 with a gas engine. The F-250 with diesel engine has less cargo rating due to the heavy engine.
So if you decide on a larger fifth wheel, then consider the F-350, it has a 4,000 pound cargo rating, much larger brakes than the F-150, and has a better engine braking system.
While Ford "Says" the F-150 will tow up to 10,500 pounds, that does not include a lot of extra weight in the truck while also towing that trailer. Consider the GCVWR of the F-150, then subtrac the trailer weight and curb weight of the truck you might only be able to have about 200 pounds of non-trailer weight in the truck besides the 10,000 trailer and 1 driver.
Fred.