Zoli
Before anyone buys a van that will be used to haul a lot of weight or bulk, they would be well advised to check the curb weight of the van and the GVWR. The difference is the capacity of the van cargo.
A Sprinter, for example, includes a typical driver and full fuel tank in the curb weight; other maufacturers may not. Check with the Ford, Chevy or Sprinter Dealer for specifics. If you buy a used van, go to a public scale and get a weigh ticket to see what your cargo capacity will be before and after you add any of the below mentioned stuff.
A Chevrolet one ton, Express 3500 Extended van has a curb weight of about 5700# and the GVWR is 9600#, BUT, after you add the many items required and desired for expediting, your safe cargo capacity is between 2500# and 3000#. Some of this add'l material may be:
Plywood floor; E-Track and other cargo securement eqpt; wood and mat'l for a sleeper; mattress and bedding; clothing; qualcomm; office supplies and container; tool box with spare parts, lamps, filters, oil, additives, wash fluid; emergency triangles, fire extinguisher; cooler with snacks and beverages; bug shields; running boards; placard holders; CB radio; spare battery(s)
An expediter should always choose the extended van over the shorter wheel base to maximize capability for relatively little extra cost. It may not seem so at first, but that extra 18", or so, will make a great deal of difference in overall comfort. As an aspiring part-time expediter/courier you might not think you'll need a sleeper in which to lay down. Consider that many runs will take you to a delivery point that is not open for 4 or 5 hours; you'll then want some quality rest not achievable in a reclined drivers seat. Also, you'll want to sleep, not just rest, prior to returning home after a 600 mile trip.
We've seen many folks that have part-time jobs to fill in the expediter down time and have enjoyed revenue from both ventures. We also have a Firefighter among our Forum membership who takes a run or two during his off-duty time, so your idea is certainly doable. Your success will be determined by your choice of vehicles and more importantly your choice of carrier; choose each wisely, apply a sound work ethic and you can make it work.