It is my understanding that if the GVWR is 10,001 or above you need to have a DOT medical card which shows you passed the same physical as the CDL holder, plus if you travel over 100 miles from your home base you have to carry a log just like the big trucks.
GM makes a 3500 series van that has a GVWR of 10,000#. They are generally 15' long. Penske uses them alot in their rental business.
That would probably be the way to go. You can usually find used ones on eBay fairly reasonable.
If anyone has any additions or corrections to this feel free to fire away.