What legalities do I need to consider when buying/selling/possessing complete parts kits that have been properly demilled?  
I plan to buy a kit and convert to semi-auto and just want to make sure I can legally possess the parts given they were part of a full auto gun prior to demilling.  Specifically thinking of Sterling and Uzi.
Thanks

They are not firearms, just scraps of metal.

Unfortunately AFT has banned the inclusion of original live barrels in the latest longarm parts kits demilling requirements, making it more difficult to do a build. Older demills can have live barrels, as the rules that existed when they were demilled were more lenient, but they will fetch a much higher premium.

As long as you stay title I, and don't build anything NFA without a tax stamp or S.O.T., as the case may be, you are good. Title I PMFs are legal to build by federal law, and in most states, be aware of your state laws though.

Selling a parts kit is not regulated, selling a PMF might be a problem for AFT if they construe you are a dealer/manufacturer without a FFL/S.O.T., and some states prohibit it. Also be aware of your states laws for serialization.

That's all I can think of atm.

Very helpful, thanks for taking time to respond.

Parts kits I in United States that are demilled in United States do not need to be touched cut, and the barrel does not need to be destroyed. All you need to do is remove a significant portion of the receiver.

Has the above poster mentioned this will cause the parts kits to be of greater value and higher demand then recent imports.

I didn't realize it was only imported kits that required the barrel be remove. Was seeing a lot of M16 type kits with no barrel, maybe those were re-imported.

Incredible wrong information right here. The current ATF guidelines for at least the last 8 years are torch cut and must be missing at least 1/4 inch of material with each cut. Old kits were bandsaw cut. That has not been the case for many many years.  You also must torch cut the barrel on current kits. The ATF has a chart for individual firearms. I think most are up to 5 cuts now.