1- Agreed.
2- If 1, then this should be automatic, as it is now.
3- Buyback programs are a massive failure. Massive.
4- No issues with this. Though it doesn't address these mass shooting events.
5- Agreed.
6- Worthless. You'll never get rid of the ones on the street already, and these can now be printed.
7- See #6
8- Absolutely.
In regards to point 3 -- there is one place where buy-back programs have been effective which is high crime urban areas. There is a proven correlation between buybacks and less availability of unregistered guns for criminals. Outside of these urban areas, I will agree with you that gun-buybacks are for the most part worthless.
In regards to points 6 or 7, not allowing the sale of these items should reduce the future numbers of them out in the streets, even if people create them at home via three D printers etc. The other route you can go is to criminalize the possession of these items, but I don't really believe in going in this direction.