Car Body shop Printers
The Materialise Mammoth printers seem to be the predominant choice for manufacturing car body parts. However, any sufficiently large printer (e.g. bigrep) could work. That said, car body parts are quite a challenge to 3D print given how excruciatingly long such large parts take (exacerbating the probability of failure). You will have to very carefully consider whether 3D printing is right for your application (it probably is not).

The licensing part is extremely complicated. You'll have to deal with patents (perhaps the body part incorporates some clever patented feature), trademarks (you generally can't reproduce manufacturer's logo's) and copyrights (if the part is very "artistic" it might be protected by copyright, but this is unlikely). A simple, functional part such as a body panel would generally not be protected by any of these but these three things are the main reason why you might need a license.

In addition, you have to be careful as to which materials you use, as these will (most probably) not be as strong/durable as those that are produced by car-parts-manufacturers. Furthermore, if you print the parts yourself, install it in a customer's vehicle, and the vehicle malfunctions, as a result, you may find yourself being sued.