Chambering actually is a lot easier these days than ever before.
At least for me, I even killed a few guys with a well timed chamber attack.
Basically all you have to do, is to release a quick counterattack to face the enemies weapon when it almost hits you, this blocks his attack while yours will still go for the enemy, most don't expect it, so it's a good way to break through defenses.
Best class? I'd put this together with your three: Learning advice.
Find a buddy, go to duel server, get wooden weapons, sticks are very good for this.
And practice while standing still first, overhead and stab are a lot easier than the side swings, but they aren't impossble either.
Also bring heavy armor if you can, makes practices longer, and forgiving.
Also if you duel people, try focusing on not to block or spam them, but to chamber them.
Sure, you might fail sometimes, but it will help you on the long run.
PS: Don't even think about using chamber techniques against people who hold or spam feints all the time. Against those, you have to get them under stress to stop doing holds and do simple attacks while focusing on blocking. From my experience and what I know, chambering holded swings in a real fight is virtually impossible. Sure, it could happen, I don't know. But it's too risky.
But I'm not a real Chamber master. Let one of those talk, might give you a better insight.