I have never had the pleasure of owning a new DSLR, but your methodology makes sense for a new purchase. I am also a manual reader and I like to have the camera in hand when I do. Reading the manual on a large computer screen is easier for that method than fiddling with the small Nikon manuals.

I never thought about a "new to me" unboxing ritual, but I think it's important to reset the camera to factory defaults when you're buying used and also checking to make sure the latest firmware is installed. This might even be important for a brand new camera depending on where you purchase it and how fast their inventory moves.

When I bought my latest used camera, I didn't test it with the Tamron lens that came with it, I tested it with a Nikon lens that I knew worked correctly on my previous camera. If I found an issue, I wanted to be sure I could isolate it to the body. Also, with a used camera I really try to put it through it's paces, feature wise; things like the live feed and manual focus switches, the mirror up position, etc.

Since I shoot a great deal of figure work, I find that any equipment purchase is a great reason to schedule a boudoir session.