With any DRW, he still needs a CDL and all the DOT crap. Trailer rated at 14k and a 3500 DRW is rated at 13k or 14k. To require CDL, it can be actual weight or combination of GVWR’s. I’m not sure where you got your information from, but it is incorrect. Loaded to capacity, he would be way over. He can get a SRW F-350/3500 with a GVWR of up to 12k and avoid the CDL, but no matter what he gets, he needs the rest of the DOT crap.
This is a good post.
Most trucks run out of payload long before their rated towing capacity, especially, with goosenecks.
The Ford. 6.2L gas is a great engine, but at 7,000 feet, the turbo might be the better choice. Generally, I recommend the gas for all towing at 15k and under (too many modern diesel issues) for everything except over-the-road trucking. Elevation being a constant issue as well as increased ability to pull and stop favors the diesel, in this case.
Your trailer is rated at 14k. That means you’ll need payload around 1,400-2,100 (tag or bumper pull) plus what you and other occupants and tools weigh. For a gooseneck you need the weight of occupants and gear plus 2,800-3,500 lbs.
in other words, having a payload over 3,000 lbs would be a good place to be, with a bumper pull and payload over 4,000 lbs, for a gooseneck. I would like to see close to 4,500, for the gooseneck.