Could someone please PEACH these Infernum race updates?

[Risen of the Pit]

I deeply enjoyed the Infernum rpg; best usage of 3.5 D20 rules that I ever saw. However, I also enjoy the 4th edition rules. This led me to try and 'update' the demon breeds and the Fallen Angels for usage in 4e... but I am not a very confident person in my rule applications. So, like the title asks, could more experienced GMs please look over my attempts and tell me whether or not they feel my work is balanced?

I'll begin with the Artificer.
Artificer
Origin: Immortal
Size: Small
Speed: 5 squares
Vision: Low-Light
Stat Bonus: +2 Intelligence, +2 Constitution
Skill Bonus: +2 Arcana, +2 Dungeoneering
Racial Features:
Born in the Flames: Artificers have Fire Resistance 5 + 1/2 character level
Unfeeling Shell: Artificers have Cold Resistance 5 + 1/2 character level
Flint and Steel: you gain a +2 racial bonus to saving throws made to end ongoing damage.
Natural Armor- you may use Harden the Shell as an Encounter power.

Harden the Shell
Iliaster pulses through veins into the metal sprouting from your flesh in response to an enemy's blow, ensuring that they will not find it so easy to hurt you with further attacks.
Encounter
Immediate Reaction
Trigger: you are successfully hit by an enemy attack
Effect: you gain a +2 racial bonus to Armour Class until the end of your next turn.