Ugh. Background checks I'm all for. Make them instant. They already are, and there is no excuse for them not to be. As far as getting mental health flags and shit into the system, that is not really a partisan issue in the gun debate. It's an individual privacy issue that has to be fought in the courts. I'm all for it, but it's not as simple as passing a law and having it done.
Waiting periods make no sense and never have. The assumption there is that somebody buying a gun needs to "cool off". What kind of horseshit is that? How many people go buy a gun to kill somebody versus the girl who needs one immediately because she has a crazy motherfucker stalking her. The whole waiting period argument is simply insulting.
National gun registry is a non-starter. No way, no how. You want to do it at the state level, then fine, but I won't be living in that state if I can help it.
I don't see a reason for limiting gun and ammo ownership either. Because some mass shooter has a couple guns? It's nobody's goddamn business how many guns a person owns. If you implement limits on gun ownership at, say, 5 guns, that means a record of it is somewhere, most likely the ATF. So now the ATF knows that you own guns and 5 of them. Seems like a good reason to be needlessly targeted by a bloated government agency with nothing else to do.
Liability is a state issue. As a mechanism to reduce gun violence, I don't see how it affects anything. Say my gun gets stolen. Whether I notice it immediately or after some fucker uses it in a crime really doesn't matter. And how liable should I really be when the weapon is stolen? That means somebody came into my house, violated the sanctity of my sanctuary, and fucking took something I own. I'm the criminal because somebody else committed a criminal act? The only way that reporting theft would help is if it stops it from being pawned. You catch the guy who stole it and tried to pawn it, but he isn't the guy who used it to shoot people. He's the guy who tried to pawn it for money. Maybe he has shot somebody before and maybe he will in the future, but he didn't then.
Again, the whole concept behind most of your ideas is control, but control in this case doesn't appear to have any real law enforcement value. If you had said just ban all gun ownership, then yeah, that would have an effect on gun violence, though I'm not sure what the effect would be on overall violent crime. Frankly, the trade-off there between perceived social security from a full-on gun ban and the restriction on my freedoms to defend myself is not worth it to me.