You can miss with the extra attack the WF gives you. The attack itself is not special though, its just a regular white dmg attack. When the totem procs for you the combat log will show a "You gain 1 extra attack from Windfury", its like an instant buff you get, not a special attack being performed.
Is Windfury considered a special ability, ex, does it suffer from a 24% miss rate or a 5% miss rate?
No. They changed that a long time ago.
Can Windfury trigger off of itself?
Yes. My warrior has had some amazing PvP kills of Sword-Spec+WF combos.
Can Windfury trigger off extra swings from HoJ and Sword Spec?
Can HoJ and Sword Spec trigger Windfury?
Oh and you asked the same question twice.
Nope. That's why shaman prefer very slow 2H weapons for WF.
Is the extra attack normalized to 1.7/2.4?