Depends on the van and bus. most buses are much longer than your original picture and most vans are not that long.

If your wanting a something to live out of then pick a cargo van to start with, that way you don't have to remove any seats since its already empty and doesn't have all the windows that you would need to cover. It will be somewhat stealthy too since a van that looks like it belongs to a plumber or electrician or phone company will probably not have any useful supplies in it.

Dual wheels don't give better traction, they give wider weight distribution. They are fine for pavement but if you need to detour off the pavement for some reason, even if just to make a U turn in the highway then your going to get stuck as they tend to float on top of the grass/dirt/mud/snow and can't dig in to get any traction. Also if your carrying a heavy enough load to need dual wheels then you don't get an instant spare if one goes flat because the remaining wheel can't carry the load by itsself so you still need to pull off and change the tire. And then the inner one is a pain to change and you have the hassel of keeping pressure balanced between the two plus the extra wear becaus on a turn the inner and outer wheels have a slightly different turning radius, thats also part of their off pavement problems too, since they are kind of slipping a little when turning its easy to break traction. Go over to some RV forums and look at the debates between dual and single wheels for people pulling large trailers or hauling large campers. They always try to get by with single wheels rather than dual so they won't loose traction when parking at the campground and once one of them has to go to duals to carry their road weight they get very limited as to where they can park and usually have to have a dry level campground as the duals can't get them up hills off pavement.