I'd suggest yopu go out and actually drive some of the base vehicles you are thinking about.
I had wanted a 101 since they were still being built. Got to drive one a few years ago, whislt I was helping to renovate it. What a truly awful vehicle. Two useable gears - 3rd and 4th. Hot as hell in the cab. Noisy. Appalling handling - even with 3/4 of a tonne in the back. Awful brakes, even re-built....and so uncomfortable. Useless off road as well - utterly useless. It's all stuff that can be sorted out. But why bother? You can't polish a turd - just cover it in glitter.
The Volvo is similar - more comfortable. Lovely engine. But anything more than a 20mile drive and your sanity will slip..
The Iveco Daily 4x4 is brilliant - designed for long journeys etc, good engine, good 4x4 system, easy to find spares across the known world. Avoid the 2.3 16 valve diesel.
Fitting a cummins 6bt in a 101 would make it drive like banana on ice. The engine is soooooo heavy.
The OM606, with an SD350 Pump is super frugal with more than adequate power - brilliant conversion...but expensive
Be simpler to buy a 130 and mode that up to be comfortable, realtive high cruising speed and relatively frugal. You can sleep 4 in the quadtech - even the lower hardbody. I had a client the other week, who was sleeping in the hardbody on a 60 plate Invincible - he had fitted electrically powered screw thread jacks in the the corners to lift the hard body 18" - using neoprene to fill the gap.
Long distance is about comfort for ALL the passengers and driver. It's about quite, sensible temp levels, easy and safe load storage, reliablity with simple fixing, frugality... Just by a VW T5