I'm sure you realize that there are several things to consider.
Is this also going to be your personal vehicle? There is a lot of space in an Ody when the rear seat is down and the middle row seats are out,,,but the middle row seats are not easy to remove and re-install.
For a service vehicle, have you considered something like a Dodge Sprinter???
http://www.dodge.com/en/2008/sprinter/