Diablo – Do you have to wear the Hellfire Amulet to get the passive

I use Fists of Thunder for the gap closer and the 10% movespeed Passive as means to get more uptime for the Vortex - that gap closer and more mobility is the difference between the vortex falling off or not, a lot of the time.

Small chance, I guess, is because your base crit chance is low. I've noticed the skill stacking up on each crit I make - and using Crippling Wave as my 2nd autoattack, for example critting two enemies with a cleave will pump the aura to 3 instantly.

Continuous is based on your attack speed as is with many other "tick" based spells.

I also use the Dodge Mantra to not have to back out of a fight since you wan't to be there, letting the Vortex work it's magic for as long as you can. I also use Serenity (absorb all damage for 3 seconds) and Blinding Light as means to keep me out of harms way while steadily grinding down waves of foes with cleaving and the Vortex.

For the Critical Mass passive, what is meant by the "chance" is that it is determined by the proc coefficient of the spell you cast. Single target spells have 100% "chance" to reduce the cooldown by 1 second while AOE spells have differing sets of proc coefficents by spell AND rune. There's a few sites that break down proc coefficents of various spells which applies to crit chance as well as return on LOH. Here, and here. Luckily people with more patience than me seem to have most spells crit proc chance figured out.

Some useful proc chances for popular wizard spells:

Hydra: 0%, Hydras never proc
Magic Missile / Seeker: 100%
Shock Pulse / Piercing Orb: 25% per target hit
Blizzard / Snowbound: 2% per tick per target hit
Energy Twister / Wicked Wind: 10% per tick per target 
Explosive Blast / Chain Reaction: 11% per target hit per explosive (of 3)

I've recently been trying the Windup Wizard/CM build which still seems pretty effective, and a bit silly (in fact it was the easiest way for me to beat inferno Ghom). From personal experience I've found that on my wizard, when I run over 40% crit chance while using a build like windup wizard, everything is off cooldown pretty much all the time.