Oh I agree 100% you can never have too much trailer as long as you are good to haul it legally which is pretty easy to accomplish with ag exemptions. I was at a trailer dealership a few weeks ago and they had a one week old used trailer for sale. It was a tandem dual gooseneck a guy bought to haul his skid steer and construction materials on. Evidently the second day he had it the dot popped him and he found it easier and less costly to trade it in at a loss and get something smaller than do everything required to be compliant. I just didn't want you to be that guy.
I have a CDL, dot number, mc number, interstate operating authority, etc. We have two pickups hauling goosenecks, a peterbilt tractor trailer, and a tandem dump truck. I probably spend close to 10k a year on the required insurance, various fees, registrations, inspections, drug testing programs, etc. It also takes a ton of time dealing with it all.
As to the 17.5's I love them. I have not replaced tandem duals with them as singles but I put them on my 14k trailers just as an added safety margin. They seem to last forever and blowouts are a thing of the past.
Keep in mind with a 3/4 ton tow vehicle you are going to be pretty limited on what you can haul on a tandem dual without overloading the rear axle and tires on the pickup. Every time the DOT has stopped me they weigh each axle and make sure we are under each axle rating and tire ratings. I don't know exactly what your truck is rated at but I am guessing the rear axle rating is somewhere around 6500lb and it probably has over 4000 on it empty which doesn't leave you much room for pin weight on a heavy duty trailer.
Just last week I ran up to Missouri from Texas and back. I saw five DOT guys with people pulled over during my trip. One had a 18 wheeler the other four had pickups pulling tandem duals. The dot knows that most semis are legal and that the vast majority of gooseneck guys just hook on and go and it is an easy revenue stream for them.