Defence cap, then (effective) health and stamina, then hit and expertise if you're lacking.
That's the order of things you'll most likely want to gear for when making a tank.
Gems are up to you but majority either Stamina stack, Mitigation stack, or a mixture of both. High-ends usually do the last one with more emphasis on Stamina because of the rigorous damage they'll take.
Enchants, you'll want survivability AND threat generation (if you can). Reason I say threat gen is because "Armsman" enchant on gloves is a very useful one at that. Otherwise Stamina, mitigation and health overall is considered as viable enchants.
Weapon, there's many enchants but the majority would see Blade Ward as a universal useful enchant.
Healing is the source of life. Without it, you're left with death.