Regarding leveling, after leveling a rogue and a mage, I found even ret leveling to be unbearably slow. So I spec'd prot and leveled mainly by tanking instances. I found that as a tank, it's extremely easy to find groups, and once you get a reputation for being a decent tank, you'll find yourself often getting group invites as soon as you log in.
Seal of Blood and Seal of Vengeance are two different abilities that paladins get around level 66 or so. The catch is that only Horde paladins get Seal of Blood and only Alliance paladins get Seal of Vengeance. Seal of Blood is generally regarded as a key ability in making ret dps viable in raids, while Seal of Vengeance is only situationally useful, and most of the time one is better served by using Seal of Righteousness. It has its uses, to be sure, but it can also be a bit unreliable.
490 defense means that you are *uncrittable*.
102.4% total dodge/parry/block/miss means you are *uncrushable*. Getting 490 defense is easy, and can be done in blues and greens. Getting uncrushable is harder, with stacking Block Rating being the fastest way to achieve it.
Defense after 490 is still very valuable, as it still increases your chance to dodge, parry, block, and be missed.
In general, the goal is to get 490 defense first, then work on stam and uncrushability. Once you're uncrushable, focus on stam primarily, while also trying to increase your avoidance (which is dodge/parry/miss).
For tanking Kara, I'd say the minimum gear requirements are 490 def, as close to 12k unbuffed health as possible, and as close to uncrushable as possible. This means getting the 15 badge Libram for sure, as well as stacking a bit of block rating. And as long as you use a wizard oil (cheap 42 spell damage buff) you should be fine with around 200 unbuffed spell damage, which isn't much considering your weapon will be 161 of that (121 dmg on the weapon plus 40 dmg enchant). Armor is a difficult thing to purposefully stack, as its largely just a byproduct of the item level of your gear. Really only the Felsteel pieces have additional armor on them. You'll probably have 14k or so when you start tanking heroics and Kara.
My advice is just to run as many instances as you can, because it doesn't matter what gear you have if you don't know what to do when you get into an instance. Practice tanking, get good at it, and you'll never have a hard time finding people to tank for.
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