Well, if the outbreak is fast, then that actually hastens the eventually collapse of the apocalypse: less time for all the zombies to rot. It might lower the chances of people initially escaping, but they don't have to fight off the zombies for that long. If everyone's infected within the first six months, then the time to no more zombies is six months plus decomposition time (around two months), so that would mean the zombies would be gone in under a year. And if everyone comes back as a zombie, then it becomes procedure to cremate your dead immediately, strapping the corpses down to do it, and life can still go on although more hazardously.

As to three and four: yes, there would definitely be panic while the zombies were there, and you'd definitely have to fight them off, I'm not arguing that. And yes, a lot of people would probably die. But there's an end to that stage, you know? There's a point within a few years when you stop fighting and start to rebuild. The world isn't permanently zombie-ridden, and I bet it would be possible for a group to outlast them.

Decaptation/headshots will definitely do it

The only reason for this to work is if the brains are a key part, even if they aren't functioning normally anymore. Otherwise, what are you removing with the decapitation? And even if they don't, in fact, need the brains anymore, ligaments decompose too, and nothing's much of a threat when your bones aren't sticking together.

A zombie apocalypse would definitely suck and involve a lot of fighting and desperation in the short-term, though!