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.
I'm not sure I agree with you on the buyback issue. Please show one buyback that was a success. All of the ones I have seen resulted in crap weaponry being turned in for high prices just because the criminal in possession needed a quick fix, and could probably steal/acquire another. Banning high capacity magazines and bumpstocks would merely raise the street price. There are quite literally hundreds of millions of extended capacity magazines on the street. Even making them criminal is useless unless you have some way of finding people who are going to use them out in the open. Ranges would just look the other way, as they do now with other illegal firearms alterations. Additionally, banning a 30 round magazine does absolutely nothing when all I have to do is tape a standard capacity mag upside down to another regular capacity mag. I can fire continuously with a 2 second (if that) pause while I flip the clip. Keeping a round in the chamber while I flip it even prevents me being vulnerable.
There are many times the Police hail gun back programs as successes simply because many weapons were purchased. This should not be the definition of success. The definition of success for gun buybacks should be if gun-related crime dropped in the six month following period in the direct local area where the buyback occurred. They will also need to differentiate the amount of cash given based on the weapon type IMO. I will agree with you that many buy-back programs have proven to be ineffective. One press example - https://www.usatoday.com/story/news/nation/2013/01/12/gun-buybacks-popular-but-ineffective/1829165/
There is a simple solution for that. All buy-back guns must be destroyed. The only exception to be made would be if a gun is turned in that has historical value and provided to a museum.
This stuff cannot be fixed. I'm all for a reduction of the violence if someone, somewhere, can propose a solution that could work. The reason no one has, is because there isn't. Not as things stand right now. Instead, focus on why people are losing their minds and going off the deep end. Stop giving them the media attention. Address mental health concerns. Things like that. Gun buy backs, confiscation, all that is a pipe dream and has no success chance whatsoever. We are simply too far down the road for any of it to work at this point. I really, really, wish that weren't the case.