A Class III license. I'm not involved in these weapons, but you'll soon get more detailed info from those in the know. I would use what you find out on this forum as a starting point. But someone, who you determine knows what he is talking about, will probably go out of his/her way to help you. Good luck.
Yes a federal "permit" is needed, but its actually more of tax filing than a permit. Do a search in the full auto forums - this topic has been gone over again and again. VUPDblue sets out the basics here: