When you're towing, max out your tire pressures, whatever is printed on the sidewalls. You can always let out air if the ride is too stiff, unloaded.
I'd suggest you keep maintenance performed, an eye on everything, and an ear open so any potential failures are caught in the initial stage. You should be OK because you're close on weights and Ford is known for durability. I would definitely not drive 70 mph, especially if the trailer has already been "swirly" once. If the trailer becomes imbalanced at those higher speeds, chance of recovery can go away quickly.
Good luck with your new rig.