Another approach since you are new to vans-
Buy this E150 for a good price and play with it as to layout, usage, etc. Get a feel for how you like it. But be very $$ prudent as to the mods. Wood and screws are pretty cheap in the big picture. Many other adds such as sinkís, heaters, inverter, water tank, etc. can be swapped to your final build rig.
I am concerned about your budget constraints- $4k to buy and do some reasonable basic interior mods is fine. You are tens of thousand$ away from a 4x4 fully converted van.
A UJOR conversion alone is going to be $15k +/-, and likely much more due to scope creep w wheels/tires/winch/air/ recovery gear.
When you figure out what you want/need, buy another van for your final build which as recommended by many here should be 1997 and up E350 or even a Chevy AWD.. It is crazy easy to be into a rig for $30k in PARTS and a small amount of contracted work in very short order. It all adds up quickly.
Beastie 3: 2002 7.3 EB Cargo: Agile TTB, CCV Mid Top, Custom Walk Through, Lots of stuff added. BlingMyRig.com