I thought my preference would be windows on the rear doors and on the side sliding door of my Ford Transit. Certainly not more windows than that, or they would get in the way of building cabinets.
However, when I bought the van there weren't a lot of options and I was lucky to get any Ford Transit in the size I wanted. The one I bought has no rear or side windows.
After doing the van build, I actually like it as it is.
I'm quite used to driving a vehicle that has no rear window or passenger side view behind the cab, (pickup truck with commerical shell on it) so I'm very used to driving entirely with side mirrors, like 25 years used to this.
I took one 6-day camping trip so far with this van I bought 1.5 months ago. Each night I boondocked in the woods, I left the sliding door wide open, even while sleeping, and this seemed quite enough visibility outside. If I wanted more visibility I could also open the rear doors.
I see a couple clear advantages to having no windows. One is that heat passes through glass more readily than through metal, so you can keep a van cooler if it has no windows. Reflectix put up against the window may not work ideally b/c reflectix requires an air gap to work, as I understand it.
Second advantage is privacy. This is not merely a "stealth" concern but also privacy when in campgrounds or boondocking in a site where others might potentially be able to look in, even just while they drive by. For instance, sometimes while en route to my destination, I end up having to camp on the side of a road somewhere, in a place where there may be others driving by. It's nicer for me if I can have a light on inside the van and know that no one can see me as they drive by, peering in at me through a window. This is not a big concern but it just feels a tad more comfortable to have the privacy.
If at some point I decide to have window/s, I believe I'd add a window to the sliding side door, but not the rear doors, as this would aid with driving too, and due to the design of my build, this would be the best option in terms of both maintaining privacy yet also allowing me to have the nicest possible view with the van totally closed.