Wow, lots of questions in there. Let's start with some basics. Keep in mind with towing there are two equally important numbers related to your truck: How much can it carry? (often called payload) and how much can it pull? (often called max towing). Be sure you are buying a vehicle that checks both of these boxes with the trailer you want.
Manufacturers and dealers LOVE to brag about one of these numbers while ignoring the other. From your post I suspect you've already fallen victim to their advertising. The "max towing" numbers they love to throw around are virtually unattainable unless you are traveling in a truck all by yourself with not so much as a latte in the cup holder. Every person, cooler and piece of firewood you put in the bed of the truck take away from that "max tow" rating.
So, the first thing I'd do if I were you is research the towing basics and how to find max payload on trucks and go from there. fwiw, in most cases, a truck's payload becomes the limiting factor - this is why manufacturers and dealers love to ignore it and focus on some tow rating that you're unlikely to ever achieve.