There was a "Family Try a Bike" event scheduled for the Venture Outdoors Festival that got cancelled and I think was supposed to be put on by 412Flock & BikePgh Spinnsters. You might want to touch base with them.
These guys do electric assist.
http://www.adamsolarresources.com/adamsolarrides.html
There are a lot of resources, check around. I'm not sure if any one shop has more knowledge specific to setting up a cargo bike like you are proposing.