A few questions.
Is a Sprinter out of the question?
Off road travel part of your plan or winter snow and ice driving in the mix?
Are you planning to camp where power and water (full shore hookups) are available as a rule?
Do you need a standalone air conditioner?
If you need a dedicated bathroom/shower, the smaller vehicles (smaller than the Sprinters) make for some cramped conditions if you want one in the van. Water and gray water tanks takes up space and requiring showers usually means quite a bit of water unless you have full hookups that many campgrounds don't have. There isn't a problem with small sized tanks if you can dump on a regular basis but designed correctly you can put in larger ones than what I have. I've yet to camp anywhere that had hookups but its not my style. I have a lot of other off road equipment that takes up space.
Having good traction in poor weather is something that's nice if you want or have to drive on snowy or ice covered roads.
I feel as a standard camper Sprinters are more suited than what I have. But where you park it at home might make a difference.
Adding air conditioning can be a huge factor. Forget a roof mount on a pop top.
Here is a good trip report that might help you on the Nissan:
This member posted some good stuff on the Nissan's and you can search his posts.