Gear and Profession questions.

I have finally reached 70 on my tankadin and I fell that I am getting geared fast. I have read most of the stickies in all the forums but 2 questions are still bothering me.

1. What is the "correct" gear level to start tanking and off tanking karazhan and how about heroics as well, with my current gear what can I tank?

2. I am currently JC/ Mining, I am having problems seeing the benefit of JC and am thinking about dropping it for engineering, is that a good idea or shoild i wait it out?

Thanks for any advice!http://www.wowarmory.com/character-sheet.xml?r=Kil%27jaeden&n=Sunnstyle

The helm from engineering is super good, with the new meta 12 def/10 percent increased block value, it is super comparable if not able to beat out the zul'aman helm, and you won't need an upgrade for a long time. Although Jewelcrafting now has some nice trinket patterns from the shattered sun offensive rep, and the epic jewel crafting only gems provide a bonus for stats and are easy to get. I think engineering provides more of a bonus just because the helm is that good, but its a pain to level from scratch.
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Paladin/70/Rivendare

http://www.blizzardguides.com/wow_1-300_engineering_guide.html

For those of you that want to level from 0-300 engineering rather quick and rather inexpensively.
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Frostmane: Danyell, War, 70 MT
Frostmane: Karahmon, Sham, 70 Elemental
Frostmane: Tazzlehof, Rog, 70 Sublty
Frostmane: Raystlyn, Mag, 70, ICE
Frostmane: Chrysianna, Pri, 70, Holy/Disp
Frostmane: Styrm, Pally, 47, Tankadin (GM)