You've got a lot of info & advise coming your way to digest, first, have you considered the cost, RV'ing isn't necessarily cheap, the Van type that you are considering is known as a Class B, Generally more expensive than a Class C, ($100 thousand +/-).
Buying a class B just so you can park on a city street, isn't why most people buy an RV, many cities have "NO overnight parking" ordinances regardless of the size.
WalMarts and the likes are generally used to stop for a few hours sleep & back on the road, NOT for "camping", again many localities prohibit even that.
There are different ways to use an RV, but just driving around and parking on the street isn't usually one of them.