Chezmoose, all of your questions are good ones -- and there are lots of answers! Over on the Boondocking and Dry Camping forum, there are discussions about fresh water, about batteries, about lighting, about dealing with gray and black water, and so forth.
If you want to get way back into the woods, a truck camper is the best option -- but it is too cramped for me. So we have opted for a little trailer. My advice is to get the smallest trailer you can stand to be in (and can stand up in). I really like the Casita and the Scamp, but most models do not have enough headroom for me.
The other issue is ground clearance -- not every trailer can be modified with an "axle flip." Trailers with torsion bar suspensions can be raised, but not a whole lot. Clearance is important on rocky roads. (But even if you have a lot of clearance, take it real slow to avoid damage.)
You want a good match between your tow vehicle and your trailer -- a trailer that is too long or too heavy will wag the dog. Coming from a PUP, you will notice a steep decline in mpg. There is no cure for that -- even a small TT creates a lot of air drag.
Be sure to take it slowly, one step at a time. Boondocking is tremendously rewarding, but there is a learning curve. Start small -- a couple of nights. Monitor battery usage. Measure water usage. None of this is rocket science.
In terms of which rig to buy, there are a lot to choose from. This is our second Fun Finder, and we are happy with it, but some other folks have had quality control issues. (There are two Fun Finder forums or clubs online -- almost every make has its own user group, somewhere.) Lance now makes a new line of small trailers -- that firm has a great reputation for building strong truck campers, so I have hopes for their trailers!
Most crucially, keep asking questions!