I alluded to it in my earlier reply, but one thing to remember is the COMBINDED gross vehicular wieght RATING.
Here in Indiana (and I assume it's fairly standard across the U.S.), if the combination of the truck and trailer is rated 26,001 pounds or more AND the trailer is rated at 10,001 pounds or more, then you need a CDL, class A. IF the combination is 26,001 pounds or more, rated, and the trailer is rated at 10,000 pounds or less, you only need a chauffer's license. This, of course, is assuming that neither has air brakes.
What it boils down to is that you can pull a 10K trailer with an F-550 (last time I checked, those were rated around 19k), for a gross combined rating of around 29k. You don't need a CDL for that. However, you tack a trailer rated at 10,001 pounds or more on that same F-550 (combined rating of 29,001 pounds), and you need a Class A CDL.
I think you are safe with an F-350 and a trailer up to about 14k, but check the ratings and your local/state regs. You probably need more than just a regular operators license if the combination is being used for commercial purposes. And a DOT number. And DOT inspection.
Lot'sa hoops to jump through. And I haven't even gotten into different license plates either!
All this stuff sucks, but a ticket (or two) sucks worse.... I'm just glad I don't have to pay for all the aforementioned stuff.
I leave that up to my boss!
Dan