For what it is worth, I am towing a 38' 5er with a GVWR of 14,000 lbs. TV is a 2005 Dodge Ram 3500, short bed, single rear wheel, 4X4 with Cummins 610 turbo diesel and heavy duty tow package. It is also my daily driver and I manage to park it with some hassles in most places around town. Fuel milage around town is about 14 mpg, on the highway @ 60 - 65 mph milage is around 21 - 23 mpg, and towing the 5er, about 15 - 17 mpg on highway (again @ 60 - 65 mph). I am just about at the limit of what that truck can handle safely. As others on this forum will tell you, any of the big diesels will pull just about anything with a hitch. The problem is CONTROLLING what you are towing. Personally, I would not even consider a unit larger than the one I have without going to a bigger TV.
As for the necessary driver's license, I would not listen to anyone except the Motor Vehicle Department in the state where you are licensed. Dealers and others will tell you anything that they believe will facilitate moving money from your bank account to theirs. The sales people at the dealership where we bought our RV swore up hill and down that no special license was necessary. Both my wife and I asked several different sales people and the answer never varied. It turned out, of course, that a Class A license (same as those required for commercial tractor-trailer drivers) is required. Indeed, every single model of the brand we purchased exceeds the weight limitation requiring a Class A license. The fact is that the vast, vast majority of people hauling these big 5 ers down the highways around here are doing so illegally. As much as anything, I would be concerned about what happens in the event of an accident and your insurance company discovers that you are driving a truck-trailer combination for which you are not properly licensed?
BTW, I now have my Class A license ... which means I can drive legally and so can my wife so long as I am in the truck with her while she is driving.
Bill