5th wheel to a Class A Diesel

If you we're comfortable towing a decent sized 5'er, you'll have no issues moving to a Class A. The class A will be easier in almost every situation. They are way easier to back up than a trailer.

I would not worry about driving one with a car behind as unless it's a very long car it will go where the MH goes... tracks inside on a turn.
By parking... at a CG it's easier than parking a 5er once you unhook the car. Elsewhere you drive through as you cannot back up unless on a trailer.
I like driving my DP better than most other vehicles because it handles well and you can see what's happening ahead because you are taller than most. Does she pull your trailer? If so she will like driving the MH better.
Now that you are retired, come on over to the dark side... you'll like it.

I do not know where you can test drive with a toad, but you do not need to do that anyway. You do not know the toad is back there. You just cannot backup when you are flat towing. I would test drive as many class A's as you can.

The FMCA rallies have driving classes.

Lazydays in Tampa, Fl has a free everyday driving school.

The RV Driving School, www.rvschool.com, teaches driving. They can come to you but it might be less expensive to go to one of their locations.

Some places will allow a test drive but I do not know of any that are set up so that you can have a test drive with a toad.
You already have experience with the length issues of a 5th wheel so driving a Class A with a toad is no different. You will not even fell the toad back there but you need to be aware of the length. On turns, if the coach clears everything, the toad will follow exactly without cutting the corner, like a 5th.