Great point. I keep going back and forth in my head about this myself haha. I have a perfectly built out Toyota but it is not suitable for full time living. There are other reasons that make me want to make the switch to a van but I won't go too in detail.If money isn't falling off trees then why are you considering this now?
But, if you are anyway, I would definitely go with a V10. A good one is going to be hard to find but cheaper and easier to find than a 7.3l.
If money isn't falling off trees then find a really clean 5.4l which is easy to do. It will get you around just fine.