A 1 ton, extended van will give the most room. You need to decide if you require/desire standing room, and consider the pro’s and con’s of each.
Window vans are safer to drive, and in my opinion safer to live in because you’ll have a clear view of what’s going on around you. My current window van was also much cheaper to insure than a previous cargo van as well.
Newer, computerized vans typically require much more in repair and maintenance costs than an older pre computerized, well maintained van. The cost of ownership and operation of diesels is roughly 3 times the amount of a similar gas engined van.
I think comfort and reliability are far more important than gas mileage. You can always drive less if your gas mileage is poor. Take the time to smell the roses. I might stay in a town for a month or more before I feel like moving, and then it’s rarely farther than a single tank of gas away, and that’s not because I am short on gas money.
My high top, extended length camper van is about as spacious as it gets without getting something larger than a van. Mine was unfortunately stripped when I bought it for $800, so I built it myself with all of the amenities you listed and more. My entire conversion probably cost about $200-$300.
One question I always ask people, is whether converting a camper van is cheaper than buying one ready made, or a motorhome. Frequently very nice motorhomes can be bought dirt cheap. Your intended usage might be an important factor, but spending big bucks on something that is likely to only depreciate in value is rarely a good idea. Comfort and reliability do not require a huge investment.
The lack of money and/or jobs are frequently dream killers. Having job skills that blend in well with traveling is your best bet. I worked construction jobs for many years and could get a job almost instantly anytime and anywhere there was a construction site. A typical job lasted from a week to several months. I’m sure there are other professions that could work similarly. Some people make their money working remotely on their computers over the internet too.
Many things to consider, but hopefully this helps a little.