Hello, I have owned RV’s for over 15 years, class C, Class A including Diesel pusher, and a 5th wheel. Your observation is correct, the front 4 to 6 feet in a motor powered RV is dedicated to driving, and you loose that as living space. Also, when camping, at least I did this, I would generally go site seeing, which in an A or C required a toad. That resulted in two vehicles registration, insurance and maintenance.
Now for your questions, first had to do with maneuvering. Yes it takes a bit of practice to “get the hang of it”. Even if you are used to maneuvering trailers, as a 5th wheel starts to turn more slowly than a trailer, but ends up much faster! A very short time and you will find it second nature and will be able to park it almost anywhere. Just take your time and you should have no problem.
You mentioned a 250 for a vehicle. Need to be careful, you need to be worried about your tounge weight rather than tow weight. This by itself can become a whole topic of conversation. I personally had a Ram 2500 with “helper springs, and was a t maximum with a 35 foot 5th wheel. Now to your question. Yes gas stations were a pain with a 5th wheel. I solved this by, one diesel pick up and a 45 gallon aux tank. I averaged 10 MPG and therefore could travel all day, (which I did not quit around 3 in the PM). And even if I were just overnighting on the way to a destination I could quickly un hook, and drive to a service station and fill up without the 5th wheel. I hope this also answers your question on hooking up and unhooking!
Very easy you back up under the hitch, most new trucks have a bed camera, push a button on the 5th wheel, plug in your cord, make sure your hitch is locked, and your off! Of course electric, water & sewer which are the same for 5th wheel or RV!
Accidents, yes they are real never speed, and drive defensively! There is a chance the 5th wheel could flip you, not a big one I would say your a lot safer in a pick up with a big Diesel engine in front of you vs a pusher with sheet metal a plastic between you and a crash! I was in my pusher and heavy winds, rocked it pretty good, in fact the slide toppers were blown open, like a jib on a sail boat once! Never felt unsafe or unstable with the 5th wheel!
Never had an issue climbing mountains, again with the diesel plenty of power going up, and engine brake coming down! I hope I have answered most of your questions.