Until you come up with a workable method to keep all these guns out of the wrong hands, your list is just wishful thinking. And you are only addressing firearms purchased legally. If our failed drug war, alcohol prohibition, music sharing, etc., is any example, people get what they want one way or another even if it's illegal. Someone willing to commit mass murder doesn't care if their weapon of choice is legal or not.
Dreaming of solutions that can only be implemented in an extremely oppressive, authoritarian society doesn't help anyone. America is vulnerable precisely because we are (ideally) a free society and only restrict those freedoms after they have been abused.
In the case of a criminal or mentally unstable person going on a shooting spree, we can and should look for symptoms and try to prevent the crime when possible. More often we are going to be stuck reacting to such crime.
I don't know about you folks, but if someone starts shooting at me in a situation like those poor folks in Florida, I'd rather be armed and trained to defend myself than disarmed and waiting to die like sheep.