Re: electrical wires, sound deadening material, insulation?…
You might be over complicating things from the start…
Sprinters tend to be overpriced, and are very questionable in the reliability department. If high maintenance costs are higher than your fuel costs, are you really saving any money? Something to consider… If it’s a high top you’re after, they can be found on many passenger vans as well.
Passenger vans already have a nicely finished interior, and they are designed for comfortable driving, and the comfort of their passengers. Many of us have learned to take advantage of that, plus enjoy the enormous savings in both time and money by starting with a passenger van with a factory finished interior. Adding tint to the windows and curtains for privacy is a whole lot cheaper than starting from scratch. You could save enough to cover your full conversion right there…
I run my electrical in PVC conduit all the way around both the floor and ceiling, with an outlet box every 2 feet. In each outlet box is 2x 12v accessory outlets, and 2x 110v outlets. Some wind up behind cabinets and things, but there is always some of each easily available. The 110v outlets are GFCI, which amounts to each having their own circuit breaker, and each 12v outlet has it’s own fuse inside the junction/outlet box. By keeping all the fuses at the individual outlets, I never have to hunt for the right fuse. You can also get 12v acc. outlet to USB converters if you need those. Not saying what I do is either right or wrong, just describing it as an option that has worked very well for me.
Best wishes for all your endeavors!