Get the sigil as its the best entry tank sigil no matter your def skill (but dont use it to cap def, thats just not a good idea and no reason too becuz...)
You need to be gemming for more def. Your avoidance is way to low. For MT of naxx 10 you need min 20% dodge and 15% parry. Def gems are the best way to get there. As of right now, your gear is fine to tank heros and OT naxx 10. There are still a few easy upgrades though, BoE shoulders from CoT strat, belt out of AN, and some easy badge loot.
I cast the spells that make the people fall over.