Only number one could work but only moving forward, the rest would never work. Your being naive about the US culture and their gun laws. Chicago has a 100% ban on guns and it doesn't matter how many police seize there are 10 times more unregistered guns with unknown ownership.
How would cops even know who to visit after a buyback? Most gun ownership is anonymous. Your practically asking for cops to engage in shootouts with civilians. Americans are literally conditioned from childhood to be distrustful of the federal government, but love the USA, they have an intense double-think of patriotism and fear and every time guns are attempted to be regulated it triggers a 1776 mentality.