Welcome to the CRVL Forum
I applaud your well reasoned outlook and researching before just jumping in.
Personally I have a high top extended Ford Van with 351 V8 & auto overdrive.
It is plenty of room for me here in my region east of the Mississippi river where
it is densely populated with numerous facilities I can rely on for laundry, gym's for
showers etc, and low cost supply sources. (so I'm basically using my rig for sleeping
or eating) In a less developed area a larger vehicle that is more "truck rugged" like a step van
may offer a better solution to live out of. If you build it out you will have plenty of insulation
and room left over. If you have to carry tools or equipment in your trade the step van may
be a better choice. You would also have room for a generator, over under laundry center,
water tanks, shower/toilet like an RV. But again this is speculation.
In my area there are lots of construction equipment operators who just find a 20' camper trailer
to tow behind their pickup truck. When on site they have extension cords to use any available
electric at the job site.
As far as manufacturers, I tend to favor Fords & GM....gasoline powered.
There are a couple of links below you may benefit from taking a look at.
A fellow I once worked with lived in the Detroit area. He spoke of going over to Windsor,
Ontario to find great deals on used vehicles.
All the best !