Your question is much bigger than you know, yet.
When I've time I'll look out some previous threads that explain, in much detail as there are so many differences, the types of Vito / Viano available.
Read lots there is a lot to understand, and buying a van that isn't suitable for your purpose is too easy.
What to understand is the difference between compact (undesirable), long and ex long.
Then there are the engine differences, essentially it is either a 2.1 or 3 litre. But the 2.1 has come in 2 guises (unless post 2018 when another appeared).
The toys in a Viano are 'generally' more than a Vito. But you will do a lot of searching if you're requirements are specific as some have this but not that. The Viano is a nicer ride, but likely to be £565 road tax (there are hints this may change and be applied to fuel perhaps, but who the hell knows they don't yet). The Vito can be as low as £140 tax, as ours.
Many if not most Viano's are ex taxis and the mileage has been corrupted on very many.
Also for the camper look up the Khyam drive away Motor Dome . We've used ours extensively and it was the best I found for purpose, although that was perhaps 6 /7 years ago.
I see there are many more options than the tent we bought at £350(ish)
But anyway it may negate your need for the pop up.
In ours I've created a bed base that is 2.1m x 1.43m(at narrowest). This folds in 3 to serve as a dining table, with under storage. It uses the 2nd row seats as support when a bed and as seats when dining.
I gave up on the idea of rotating front seats (any) as I prefer to use the between seat area for a storage unit I've fitted. It serves massive advantage while on the move.
Methinks these are early days of research.
