A person needs a SOT and a FFL is they want to deal in NFA items.
Anyone can get a NFA item (if they live in a state that allows it, and they could afford it and are not prohibited) without a FFL or SOT.
A FFL and SOT is not needed to get NFA items.
A C&R can be used to receive C&R items interstate. A C&R can be used to acquire C&R NFA items, all NFA rules apply.
You can buy a 50 year old machine gun in the next state over (without a dealer) but you still have to go through the NFA stamp process and use your C&R for the interstate part.
Q: May a licensed collector obtain NFA firearms in interstate commerce?
Only if the firearms are classified as curios or relics, are registered in the National Firearms Registration and Transfer Record, and are transferred in accordance with the provisions of the NFA.
[27 CFR 479.83 – 479.86]