Get the biggest and newest that you can afford, the closer you can come to paying for it cash the better. You will be living in this machine, so get it insulated. I use 3/4 inch foamboard, truth is I should have gone 1-1/2 inch. Get a good heater, winters can be brutal and you'll find that running the engine to keep warm doesn't work as well as one might have hoped. Everybody here swears by Espar heaters, with Webasto coming in a close second.
I drive a Chevy standard-length 2500 heavy, it has the 8600 GVWR. It's about the smallest, lightest weight that should be even considered, next time around if God allows I should consider the 3500 extended van. The heavier capacity would allow for a bit of leeway in terms of what I can put in and still have suitable weight limits, and the extra 18 inches or so can be a godsend when you have to store your stuff and find room for large freight.
Get used to the idea that you'll do more "standing by". There's not as much van freight as there is straight-truck freight, and because it's easier to get into this field in a van there's a lot more vans competing for the freight.
